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In our opinion, the best customer is an informed customer. There comes a time when you want accurate information about specific pool problems or questions. Although these issues don't always deal specifically with our chemical treatment of the pool, we feel it is important to be your resource for all possible aspects of pool ownership and maintenance. Pool Chlor has therefore developed an extensive computerized resource library covering virtually every aspect of pool chemistry, drawn from our own studies and research, as well as industry books and magazines, technical publications, governmental guidelines and regulations, etc. This resource assists our managers in finding the specific documentation dealing with practically any question you may have. In addition to answering questions utilizing our extensive chemical and general pool knowledge, we have also published technical bulletins which we provide at no charge to our customers. These bulletins cover subjects ranging from plaster stains to algae control, from pool covers and cleaners to product safety, from filters to why blondes get green hair from the pool. Interested? Just give us a call!

Topics Covered
Just click one of the topics below for more information.

The water clarity tripod: Filtration, Circulation, and Water Balance.

Methods for Decreasing Calcium Scaling

How to Get Rid of Yellow (Mustard) Algae

Why do blondes sometimes get green hair after swimming?

Fiberglass: The "Black Plague"

What are Total Dissolved Solids (TDS)?

What about those blue bubble "solar covers"?

What causes eye irritation?

What are those ugly calcium growths on my plaster?

Whats the difference between ammonia-based and copper-based algaecides?


Topics With Related Information

The water clarity tripod: Filtration, Circulation, and Water Balance

The Water Clarity Tripod - Water clarity is dependent on three factors: proper water chemistry, sufficient and effective filtration, and good circulation. Like any tripod or three-legged stool, the whole thing falls over when any one of the three factors fails.

Water chemistry - If the pH or alkalinity levels are out of balance, turbidity can be a result. Also, if there is insufficient chlorine in the water, small, suspended algae and bacteria can result in turbid water. Any of these problems can be readily fixed, usually in a single visit.

Filtration - The job of the filter is to remove suspended solids from the water. These solids may be large enough to see with the naked eye, such as leaves, twigs, and other debris. Or they may be so small that many, many of them are required for the pool water to appear cloudy. The filter can remove any of these solids. It cannot, however, remove from the water anything that is actually dissolved, and thus a part of the water itself. For instance, dissolved metals such as copper or iron can tint the water aqua or tan, but remain dissolved and thus unfilterable (unless a chelation chemical is added to clump the metal and take it out of solution).

The amount of time it takes for a filter to clear dirt, dead algae or bacteria, and other suspended solids from pool water depends on the type of filter, its maintenance, the amount of time it runs, and the circulation of the pool. DE filters are the most efficient (rated at being able to remove anything larger than about 3 microns), cartridge filters are the next most efficient (rated at about 15 to 20 microns), and sand is the least efficient (rated at about 25 to 40 microns). If properly sized for the pool, and with everything working right, all three are capable of maintaining a clean pool clean. However, they may differ drastically on their abilities to clean a dirty pool. In the winter, a residential pool filter runs an average of a few hours per day (but also runs continually when there is any danger of a hard freeze), and an average of 10 to 12 hours during the swim season.

Circulation - In order for the filter to remove solids from all of the water, the water must be circulated "top to bottom" and "round and round." In most pools, this is accomplished by splitting the suction between a surface skimmer and a bottom main drain, as well as by aiming return water in a manner to circulate the water around the pool. Circulation patterns are drastically affected by the shape of the pool, the locations of the drains and returns, and the strength of the return water flow. Pools should be designed and function in a manner which eliminates "dead spots" of uncirculated water.


In order to maintain proper water clarity, the pool water must receive adequate filtration. Sufficient filtering time is a function of heat and usage. While 2 to 3 hours daily is usually sufficient for the winter months, 10 to 12 hours daily is generally required during the peak summer months.

An overly dirty filter can reduce the effectiveness of your filter by up to 80%. Accordingly, you could run a dirty filter for 10 hours and receive the equivalent of only 2 hours of "efficient" filtration.

Most filters should be backwashed when their pressure rises 8 to 10 pounds. You should also double-check the accuracy of your filter gauge by feeling the force of the flow of water from your return line in the pool. A weak flow means that its time to backwash.

For those with DE filters, you should know that backwashing only cleans the filter grids about 50%. You're better off taking them out and washing them off, achieving 100% cleaning. This procedure should be done early spring and mid-summer. Also, the proper amount of DE to add is calculated by the following formula: A one-pound coffee can of DE for every five square feet of filter area (i.e., 45 sq. ft. of filter area = 9 coffee cans). Every 4 to 5 years it is wise to acid-rinse the D/E filter grids to remove accumulated calcium deposits which can restrict flow through the grid material. To acid-rinse the grids, fill a large, clean plastic trash can with water, and add 1/2 gallon of regular (muriatic) pool acid. Soak each grid for 5 to 10 minutes, and then hose them off thoroughly.

FOR THOSE WITH SAND AND CARTRIDGE FILTERS, YOU CAN IMPROVE YOUR FILTERING EFFICIENCY UP TO 50% BY ADDING 2 COFFEE CANS' WORTH OF DIATOMACEOUS EARTH (DE) TO YOUR FILTER! This is accomplished by adding the DE through the skimmer with the pump on, and stirring it in the skimmer until it is totally dissolved. Following the eventual backwashing of the filter, you may recharge the filter with more DE.

FOOTNOTE: DE is a very inexpensive and relatively harmless powder available at virtually any pool supply store. With normal usage, it will not harm grass, plants, etc.


Methods for Decreasing Calcium Scaling


The mineral content of your water increases every day. This is due to evaporation which removes only distilled water and leaves the minerals behind. In time, these minerals begin depositing on the walls of the pool and we call this gradual buildup "staining."

Among the options available to the homeowner are the following:
Drain and acid wash the pool periodically. Chemically remove these minerals before they have a chance to deposit out on the plaster. These chemicals are known as "chelating" agents, which comes from the Latin word CHELAE which refers to the pincer-like claws of a lobster. Accordingly, the chelating agent "grabs" these extraneous minerals and holds on to them until they are finally removed by the filter. Mechanically remove these minerals before they have a chance to deposit out on the plaster. The type of filter required to remove minerals and heavy metals is called a nanofilter. It will clean the water to "bottled water purity" without having to drain water from the pool. Once the pool water has been cleaned with the filter, a chelating agent can be used to maintain the water in a "soft" condition.


Acid washing prices vary tremendously from $95 to $450 for the same job. It is always a gamble because you cannot monitor the competence of the person performing the task. Depending on the deposits and who is trying to remove them, you may get a better job for $95 than $450! After nearly 20 years of research, we have developed a truly effective chelating agent. A quart per month should be added during the summer months. Cost - $8 per quart.

An additional benefit of using a chelating agent over acid washing is that during an acid wash, the surface of the plaster can become somewhat "gritty" as the cement is washed off, thus exposing the aggregate (sand) which is the primary ingredient of pool plaster. The acid also occasionally reacts with impurities within the plaster, thereby producing colors in the cement that are even more unsightly than the ones which were to be eliminated in the first place. Accordingly, acid washing is at best a calculated risk. Nanofiltration costs $120 per day. Most pools require one and a half to two days of filtration. If done annually, one day is enough. The filter will remove 300 to 400 ppm of calcium hardness per day from a 15,000 gallon pool.


Chlorine and filtering can keep the water "sanitary" and crystal clear, however, they DO NOT MANAGE OR CONTROL MINERALS OR METALS. This is a completely separate and unique issue which requires a totally different set of chemicals.

Chelating agents, nanofiltration, or the two used in conjunction are the best form of preventive maintenance and are really inexpensive for the results obtained. For example, four years worth of chelating agents:
$8 per quart for 6 months per year = $48 per year x 4 years = $192
Four years of nanofiltration:
About $180 (first year), $120 per year (next 3 years) = $480
Four year filtration/chelation combination:
$180 initial treatment + 3 1/2 day treatments of $60 each + $96 for 1/2 normal dose of chelating agent = $456
One acid wash every four years:
$95 to $450 (with resulting plaster degradation)


You should strongly consider chelating agents or nanofiltration as a valuable resource for protecting your expensive backyard investment. Chelating agents will gradually soften the water and inhibit calcium deposition, nanofiltration will immediately soften the water, and the two in combination will give you soft water and reduced staining.


How to Get Rid of Yellow (Mustard) Algae


(Also sometimes referred to as brown, green or mustard algae)

The Pool Chlor system of chemical care guarantees a crystal clear, algae free pool. However, occasionally one of our pools will experience yellow algae.


There are five primary reasons for yellow algae:
Yellow algae can develop when no chlorine is present. For example, when the spa portion of a pool is heated, the chlorine will often be completely used up. If the circulation is not immediately restored from the pool to the spa, the spa will remain without chlorine and algae can form. Yellow algae thrives in shade. Accordingly, a pool cover which is seldom removed can provide a challenging environment to prevent algae. Yellow algae can build up a resistance to chlorine and may occasionally require an algaecide to eliminate it and prevent additional growth. Inadequate filtration—either from filtering too short a time period OR filtering with a dirty filter—can spawn yellow algae. Most strains of yellow algae are introduced via an airborne spore that is especially prevalent during rainy seasons. It is therefore most common to see this type of algae immediately after rains.


Immediately after using the spa, turn the valves so that the pool water will flow into the spa for 20 minutes, thus rechlorinating the spa. Remove your pool cover one day per week to allow the water to "breathe." Call Pool Chlor immediately if you ever see any yellow algae so that we can take any additional needed steps. Make sure that you are filtering an adequate number of hours for the appropriate season. (Winter 3-4 hours, summer 7-12 hours). Also, make sure your filter is clean and your return lines have strong water flow. After chemical corrections, brushing the dead algae from the walls assists the filter in removing the dead algae bodies.


Although yellow algae is approximately 90% preventable, it is 100% curable.

What about automatic pool cleaners?

The Financial Advantages of the Automatic Pool Cleaner:

Question: How much do you pay someone to vacuum your pool?

Answer: Usually $35.00 a month. (For example, the difference between our chemical service and a full service is usually $30 to $40 a month).

Question: How many months would it take for an automatic cleaner to pay for itself?

Answer: Less than a year and a half. Most cleaners cost $400 to $500. Accordingly, $35 a month for 18 months equals $630, more enough to buy almost any cleaner.

Question: How much money could an automatic cleaner save you in 10 years?

Answer: 10 years @ $35 a month = $3500.00

Question: What could you buy for $3500.00?

Answer: You decide.

Additional Benefits over a once-a-week full service cleaning: The pool is cleaned every day instead of once a week. Even after a windy day, the pool will be clean. Saves time because you don't have to call your full service company and tell them that the pool is still dirty after they supposedly cleaned it. You hedge against inflation by avoiding full-service price increases.


The proper automatic pool cleaner is cost effective and very efficient. Call us for a free trial demonstration.


Why do blondes sometimes get green hair after swimming?


Occasionally blonde swimmers have a problem with hair discoloration after extended swimming. The hair takes on a green deposit, sometimes referred to as a tint. This phenomena is blamed on everything from rusty pipes to hair color preparations to chlorine. The actual culprit, however, is almost always copper.

Copper can be introduced to the water in many ways. The primary sources are:

Trace copper in the water supply, copper bleed from brass pumps or piping, copper fittings or piping, or gas heater coils (which are solid copper), copper in copper-based algaecides.

The green tint is not associated with either rusty pipes or pool sanitizers. The oxidation process is similar to that of any copper object left out in the sun and water... it makes green "copper oxide."

Actually, this problem is not unique to blondes - if the copper is present in the water, it adheres to hair of any color. It is usually only seen on blonde or light red hair because other hair is too dark for the deposit to be visible.


As far as the immediate hair problem is concerned, a rinse or shampoo with a slightly acidic pH will strip the copper deposit off of the hair. Many drug stores carry commercial shampoo or creme rinse preparations for this purpose. If they are not available, the home remedy is to use lemon juice or vinegar to rinse the hair.

A long-term solution for the pool is to chelate or filter out the copper from the water, and to see if the source (the algaecide, or copper or brass in the system that may be deteriorating) can be removed. Call POOL CHLOR for more information about chelation chemistry or nanofiltration to remove the copper from your pool water.


Fiberglass: The "Black Plague"


A common problem with fiberglass pools is that after aging they may begin to suffer from the "black plague."

Most fiberglass pools are coated on the inside with a clear layer that is called "gel-coat." This layer protects the fiberglass material from exposure to water, pool chemicals, UV light, etc. Depending on the thickness and quality of this material, it may begin to wear down after time. As tiny, invisible "pinholes" develop in thinner, older gel-coat, water, and pool chemicals can react with cobalt in the fiberglass mixture to form a cobalt crystal. The appearance of these crystals has nothing to do with the pool cleanliness, sanitizers used, or other water chemistry. It is strictly related to the product/materials of which the pool is composed.

Once these cobalt spots have begun to form, they become visible to the eye as a dark brown or black crystal, about the size of the head of a pin. If left alone, they slowly grow in size, and they start to develop a "rust" ring around them. If on a vertical wall of the pool, this ring then streaks 1/2" to 1" down from the crystal.


To remove these crystals, you can scrape them off with a butter knife or a putty knife. The "rust" ring can be removed with a rubbing compound, or with a mild muriatic acid/water solution (start with about 1 part acid to 10 parts water, and slowly strengthen if needed.)

For an intermediate-term solution, commercial preparations specifically formulated for this problem are available at most pool retailers. They carry a variety of brand names, containing the word "cobalt" coupled with such words as "remover" or "cure." They are usually very effective in the treatment of cobalting, and most can be used in maintenance doses to prevent further buildup. If the problem is especially severe, standard chelating agents may also help.

The long-term solution is for the pool interior to be re-coated, with newer coatings that usually do not have this problem. This is, of course, an expensive undertaking, reserved normally for only the most severe cases.


What are Total Dissolved Solids (TDS)?


One of the measurements that can be taken on swimming pool water is the Total Dissolved Solids level, or TDS. TDS is a measurement of virtually everything dissolved in the water that is not H2O. This includes such components as salts, minerals (like calcium and magnesium), sulfates, silicates, organic and inorganic materials, tanning lotions and oils, sweat, saliva, urine, soap, deodorant, hair spray, colognes and perfumes, plant pollens, pet wastes, spilled food and soft drinks, dirt, lawn and garden fertilizers, etc. Wow! There is quite a lot of dissolved material in that water that is still clear to the human eye!

As water evaporates from the pool, the TDS increases because the sun only removes distilled (pure) water and leaves all of the dissolved solids behind (like when you leave a glass of water outside to evaporate, the white crust left behind was "dissolved solids"). The "fresh" water you then use to replace the evaporated pure water also contains its share of dissolved solids. Normal evaporation rates are usually up to 1/4" per day in the winter and 1/2" per day in the summer. Therefore the water in the pool is continually getting "harder", or higher in dissolved solid content.

High TDS can be a problem because they interfere with pH, hamper chlorine's ability to affect bacteria and algae, create hazy water, contribute to the corrosion of metal piping systems, and promote scale deposition on the plaster and tile.

In swimming pool applications, TDS is normally measured by means of a meter that passes electrical current through the water. Since most anything that is not pure water conducts electricity, and since pure distilled water does not, the amount of electricity that passes through can be read as a level of TDS.

Tap water TDS can range from 300 to 700 parts per million TDS. The average in swimming pools is usually 1000 to 2000 ppm. The National Spa and Pool Institute (NSPI) recommends an upper limit of 3000 ppm.

TDS can be lowered through full or partial draining and refilling, through the use of chelating agents, or through special nanofiltration. If you wish to know the TDS level in your pool water, or if you are interested in chelation or nanofiltration, please call your POOL CHLOR office.


Some of the most commonly asked questions regarding pool filters are: What kinds are there? What are the differences? Is one more efficient than another? When installing a new filter or replacing an old one, which filter do you recommend that I use?

We offer the following information to answer these questions and hope that it may be helpful to you in understanding the issues and our recommendation.

Sand Filters:

The outside of this type of filter is usually made out of fiberglass or stainless steel, and it is partially filled with silica sand. As water circulates from the pool through the filter, water enters at the top and percolates downward, leaving most of the oils, debris, and other impurities trapped in the sand, thus allowing clean water to return to the pool. The filter is usually backwashed once per week, a process which reverses the flow of water through the filter. This lifts most of the contaminants from the sand and washes them out the backwash line, along with a volume of water. Eventually the filter becomes overburdened from minerals in the water and from the volume of debris (dirt, dead algae and bacteria, etc.) remaining in the sand, causing the sand to be hard and compacted. This reduces water flow throughout the system, and can cause cloudy water, poor heater operation, and increased wear and tear on the pump. Approximately every 3 to 5 years the old sand will need to be removed, and new sand added. If the pool is painted, the sand may need to be changed annually. The efficiency of the sand filter, as measured by the largest-sized particle that can pass through it without being caught, is 40-50 microns. (A micron is a millionth of a meter.) In the past, more sand filters have been installed in some areas because of the supposed "ease of use" for the pool owner, but drawbacks of the sand filter include: Longer hours of operation are required to properly filter the pool water. Filtration efficiency (compared to other types of filters) is inferior, especially in hot climates. Higher chlorine levels are usually required on pools with sand filters to help reduce the risk of the pool water turning green. Because of frequent high-flow backwashing, this type of filter wastes more water. Since homeowners rarely see the inside of the filter, and since the sand usually lasts for years, maintenance on sand filters is frequently neglected.

Cartridge Filters:

Cartridge filters come in various sizes and shapes. Most of the filter canisters (or tanks) are stainless steel, but some are made of a hard plastic or fiberglass. There may be as few as one or as many as fifteen or more cartridge elements inside a cartridge filter. The cartridge elements are cylindrical, and made of a paper-like fiber. As the water passes through the elements, impurities are collected on the element material. Cartridges remove smaller debris from the water than sand; its micron rating is about 20 microns. This filter is cleaned about once a week by removing the elements from the canister and hosing it off using a high pressure nozzle. Drawbacks for the cartridge filter include: most cartridge filters are for smaller pools and spas containing approximately 12,000 gallons of water or less; there is no mechanical method for backwashing these filters - it must be done by manually disassembling the filter and hosing it off weekly; the cartridge elements need to be replaced as they become old and worn, about every 2 years, which can be expensive, depending on the size, style and brand of cartridge; pools with cartridge filters tend to develop high dissolved solids levels (TDS) faster than sand or DE filters, because there is no water removal via backwashing.

DE (Diatomaceous Earth) Filters:

The majority of DE filters are made of stainless steel, with a few being made of fiberglass. The elements inside consist of a series of plastic grids covered with a cheesecloth-like fabric. A white powder, known as DE, is added through the skimmer and mixes with the water as it heads toward the filter. As the water passes through the filter, the DE powder coats the outside of the elements. This coating traps microscopic impurities which cannot be trapped by sand or cartridge filters, and therefore provides better water clarity in the pool. The efficiency rating of a DE filter is about 3 microns. This means you can filter anywhere from 15% to 50% less per day, which results in reduced electric bills, and extended motor life.

Especially in drought areas, DE filters are most commonly recommended and installed because of the lower water requirements for cleaning (compared to the sand filter)

Drawbacks for the DE Filter:

To clean this type of filter, the filter must be taken apart in order to hose the elements off with water. Each time you backwash, or clean the grids, you need to re-charge the filter by adding two to four pounds of the DE powder (which is very inexpensive) through the skimmer. However, since modern DE filters can go as long as 6 months to a year between cleanings, this is not much of a drawback! Older DE filters usually are cleaned quarterly.

Summary and Recommendation

If you pose the questions at the start of this bulletin to someone who doesn't regularly maintain swimming pools, you might receive a wide range and variety of answers. But if you ask a trained service technician who services pools daily, and who is responsible for the cleanliness of your pool and the clarity of the water, you will consistently hear the same answer: DE filters (Diatomaceous Earth) are the best! If your filter is working fine, there is obviously no need to replace it, but if you are faced with the need to install a new filter or replace an old one, please consider the following points:

All three types of filters are used within the pool industry. The warmer the pool water becomes, the more efficient the filter needs to be. Sand and cartridge filters work best in cooler climates, but in the western states, where pool water temperatures often reach the 90s, they aren't nearly as effective as DE filters. The cost differences between the sand and DE filters are minimal, with cartridge filters being the least expensive. If you are looking for dollar value without headaches, the DE filter will give you that and more! A DE filter requires less time and effort to maintain in optimum working condition. Although most problems experienced by sand and cartridge filter owners are caused by improper maintenance, even a perfectly maintained cartridge or sand filter cannot match the efficiency of a DE filter. As measured by the size of particle it can remove, a DE filter is 7 times more efficient than a cartridge filter, and 15 times more efficient than a sand filter. A DE filter is the best choice for those who must keep the pool clean and clear, for those who swim in the water, and for those who enjoy the look of sparkling, crystal clear water in their backyard pool.


What about those blue bubble "solar covers"?

"Blue bubble"-type solar covers are becoming increasingly popular for residential swimming pools. They provide "free" solar heat from the sun, as well as keeping some of the seemingly ever-present dirt and debris from getting into your pool. With proper care and use, they are an excellent investment. In this bulletin we would like to review some issues related to the use, care, and life of this type of cover.

Solar covers can increase the temperature of the pool by 10 to 12 degrees, depending on the amount of direct sunlight on them. During the coldest part of the winter this may not be enough to make the water swimmable, but used in conjunction with a gas or solar collection unit, it can provide substantial cost savings. During the marginal swimming periods, in early spring and late fall, this 10 to 12 degree difference can be enough by itself to make the pool water swimmable.

Follow the manufacturer's instructions regarding storage of your pool cover when it is off the water surface. Most warranties specify that they be stored out of sunlight, and that they not be left on the pool deck when removed from the pool. Note that Pool Chlor folds back a portion of the cover, as opposed to pulling it up on the deck, when servicing the pool; and then recommends that it be left that way for an hour. We will not pull it up onto the pool deck because of the warranty concern: the concentrated heat reflected by the deck can weaken the cover material. If the cover is to be left off the pool for extended periods of time, use the opaque plastic bag provided with the cover, or use large, dark plastic garbage bags to protect the cover from the ultraviolet rays of the sun, a known cause of cover deterioration.

Avoid the temptation to use the cover as a dirt barrier by simply covering the pool and leaving it covered for the entire winter. The use of a pool cover in this way seems to provide a psychological justification for skimping on the cleaning and brushing of the pool. However attractive it may sound, if you leave the pool covered for extended periods of time you will uncover the pool in the spring to find rough, discolored plaster. Putting a barrier between the water and the air deprives the water of gasses it usually maintains in a dissolved state (such as CO2). This deprivation is conducive to scaling. To avoid this problem, make sure to expose your pool surface to the air for a number of hours on a regular basis—one full day (8 to 10 hours) a week is usually sufficient to restore the dissolved gas balance.

Years ago, bubble solar covers cost hundreds of dollars and lasted half a decade. Now, covers typically cost less than 100 dollars, and last 1 to 10 years. Do they make them like they used to? No. Due to an extremely competitive market and the proliferation of low-cost low-end covers featured in retail pool store sales, covers are now made of thinner, cheaper material than the "good stuff" they used to be made of. This is not an indictment of cover manufacturers, but a description of market economics. As a result of this change, warranty periods have been reduced, and covers just don't last as long. One manufacturer we talked to said that he could make covers as thick and long-lasting as he used to, and fully warrant them for 5 or more years; but he also said that the price for such a cover would be around $500, much more than pool owners would be willing to pay. Realistically, the solar cover you purchase today will cost about $60 to $100 depending upon the size of your pool. The cover life, based upon one year would be calculated as COST divided by 12. If the cover lasts longer than the year, consider it a bonus. When you consider an amortized monthly cost of between $5 and $8 per month for the added value of water conservation and solar heating, you will still find these covers to be quite useful. The prorated warranties on solar covers are not a guarantee of how long the cover will last, but rather a means for the seller to insure your continued purchases of their covers, since the small prorations are typically not given out in cash, but taken off of the cost of the new cover. Essentially, the modern solar cover is a throwaway item. Although today's covers look similar to the covers sold ten years ago, they are quite different. The trade-off in price for the new cover also is a trade-off in overall life and durability.

There is a limited warranty on all bubble style solar covers sold on the market today. Although there are a variety of terms available (for example, one year full, two years prorated, etc.) essentially the warranty covers defects in workmanship - not product deterioration. Although details vary, virtually all such cover warranties, regardless of the manufacturer or length of warranty, come with three types of disclaimers that effectively nullify the manufacturer's liability for collapse or disintegration of the plastic cover. These three disclaimers address the adverse effect of NORMAL chemistry and temperature on the cover.

1. Warranty disclaimed if chlorine level is above 1 ppm.

There are many variables involved in the chemistry of chlorination. Limiting the technical chemistry to a discussion of water disinfection, the 1 ppm parameter virtually disclaims any pool in the Southwest. Chlorine demand can and usually easily exceeds 1 ppm; there are no references to the relationship of free chlorine to combined chlorine nor ionization ratios of the chlorine molecule in relation to pH factors. The addition of liquid, granular, tablet, or gas sanitation products will cause a proportionate and dramatic increase in chlorine levels. All chlorinating compounds disassociate into exactly the same disinfecting agents, regardless of the method or form of application. There are no chemicals that represent greater hazards than others. In the real world the 1 ppm level is unrealistic and does not conform with accepted standards for pool sanitation, since at a normal pool operating pH between (7.5 and 8.0) and in the presence of stabilizer, (conditioner or cyanuric acid), the actual free chlorine needed to sanitize the pool is only 15 to 40 percent of the total chlorine reading. Thus, there would never be enough chlorine to even meet the minimum Health Department standards.

2. Warranty disclaimed if water temperature exceeds 88 degrees

The gradient heating effect of a solar blanket will invariably cause the layer of water immediately below the cover to be the hottest level, resulting in temperatures that also exceed this parameter.

3. Warranty disclaimed if cover is stored in ultraviolet light

Ultraviolet light is a component of sunlight!

The cover manufacturers are not trying to rip off the buyer. They are simply providing a legitimate warranty against defects in workmanship, not normal product breakdown given the application. Unfortunately, many distributors are unaware of the limits of the disclaimers and the focus of the warranty on workmanship. If you check your solar cover, you will find it to be made of either 4, 6, or 8 foot sections, seamed together. The average warranty actually covers the workmanship involved in the heat seaming of the cover sections, not the deterioration of the cover over a specific time.


Again, you can maximize the life of your cover by: A) Folding back or removing it when the chemicals are applied, B) whenever you remove your cover, be sure to cover it and not leave it unprotected in sunlight, and C) if your water temperature exceeds 88 degrees, remove the cover. Also, you can protect the surface of your pool by allowing the water to "breathe" at least one day a week, thus replenishing the dissolved gasses in the water and avoiding a potential "scale promoting" condition.

Industry Quote:

"We have no reason to believe that gas chlorine has any more of an adverse effect on solar blankets than any other sanitizer, assuming all other factors, i.e. pH, total alkalinity, etc. are maintained at generally prescribed levels." Cantar Corporation, a manufacturer of "blue bubble" solar blankets.


What causes eye irritation?

Eye Irritation

Red irritated eyes, sometimes in conjunction with dry, itchy skin, are an occasional occurrence in some swimming pools. There are a number of possible explanations for the irritation when it occurs, some of which are actual causative factors and some of which are popular misconceptions.

The most popular misconception about eye irritation is that it is caused by excess chlorine. The most common actual causes of eye irritation are chloramine buildup, pH imbalance, high total dissolved solids, or a combination of those factors.


Chloramine is a chemical combination of ammonia and chlorine. Although chlorine is a desired component in pools, ammonia is unnecessary and unwanted, since by combining with the chlorine it slows down the chlorine's activity (i.e., the length of time it takes for the chlorine to oxidize contaminants). Also, chloramine is an irritant to eyes, skin, and other parts of the body. An unsavory aspect of pool chloramine is its origin: the ammonia in pool water is usually a result of sweat, spit, mucous, urine, bird droppings, dog wastes, vegetation (tree leaves, pine needles, pollen, etc.) blown into the pool, lawn and garden fertilizers accidentally introduced to the pool, and even from some types of pool chemical algaecides. As a result of the unfortunate source of swimming pool ammonia, the chloramine is not only irritating and slower acting than pure chlorine, it also has a distinctive "rotten chlorine" odor. This odor is the source of the misconception that too much chlorine is the cause of the irritation. You may have noticed this odor when walking into some health clubs or other indoor pool areas. This can be attributed to decreased air circulation (compared to outdoor pools), the high use (leading to less frequent superchlorination because of difficulties in scheduling "down time") and a larger source of organic waste (because of the heavier bather load).

Another characteristic of chloramine is that it changes in composition relative to the pH of the water. The lower the pH, the more of an irritant the chloramine becomes. Since low pH in and of itself can be an irritant (as noted below), low pH in conjunction with chloramine is even worse.

The cure for chloramine is to add enough of an additional oxidizer to burn out the ammonia. This process can be accomplished with more chlorine - roughly 7 to 10 times as much chlorine as ammonia. This process is referred to as superchlorination, or breakpoint chlorination (the addition of chlorine to the point that it breaks the chloramine bond and destroys the ammonia...). Alternatively, non-chlorine oxidizers such as the oxygen-based shock chemicals (potassium peroxymonosulfate or monopotassium persulfate) may be used.

Low pH

Another cause of eye irritation is low (acidic) pH. Since the eyes are protected by fluid (tears), the altering of the chemistry of that fluid affects the eyes. An example of this principle is the use of alkaline eye drops to ease tired, irritated eyes. Eye irritation caused by low pH can be remedied by properly balancing the alkalinity and pH levels in the pool. Low pH can also cause irritation to the ears, nose, throat, and other mucous membranes.

Total Dissolved Solids (TDS)

A third causative factor for eye irritation in swimming pools can be a high level of dissolved material in the pool. An acceptable amount of total dissolved solids (TDS) may be as low as a few hundred parts per million (ppm) and as high as 2000-3000 ppm. When levels exceed 3000, results may include eye irritation, cloudy water, and difficulties in maintaining water balance. Meters are commonly used to measure the TDS of a pool, but a do-it-yourself test is to simply open your eyes underwater. Pool water with excess TDS may be crystal clear when looking at the water from above, but when you open your eyes underwater it is usually turbid (cloudy or hazy). (Note that turbidity that is visible even when viewed from outside the pool is usually caused by inadequate filtration or unbalanced chemistry.) If you suspect high TDS, call Pool Chlor for TDS testing of the water, and request technical bulletin #7 for more information.


Eye irritation, whether caused by chloramine, low pH, high TDS, or other factors (or combinations of factors) is both preventable and curable. Although extended swimming may irritate eyes, irritation that occurs after only short periods of swimming need to be investigated and remedied. If you experience such irritation, give us a call and we will determine the cause and prescribe a cure.


What are those ugly calcium growths on my plaster?

Calcium Nodules

One of the most disconcerting experiences a plasterer can have is when he does what seems to be a perfectly good job of plastering a pool, only to be called back out to find that the plaster had developed calcium nodules (see sidebar on Terminology). Although in times past some have attempted to associate nodules with the general chemistry of the pool water, research has shown that the cause of nodule formation is cracking (from over-drying of the plaster) or bond failure (aka delamination), which occurs primarily in replastered pools.

Plaster and Water

In order to understand the process of nodule formation it can be helpful to consider what happens when you first fill a plaster pool with water. As the plaster hydrates (cures) chemical reactions take place which result in the release of soluble calcium into the pool water. This calcium, in the form of calcium hydroxide (Ca(OH)2), has a very high pH, which in turn raises the pH of the entire body of water in the pool. The soluble calcium hydroxide reacts with bicarbonate (HCO3-part of the pool's alkalinity) in the water and converts to a non-soluble form called calcium carbonate (CaCO3), which is precipitated throughout the pool in a powder commonly referred to as plaster dust (see chemical reactions sidebar). The plaster dust is brushed and filtered, removing it from the pool. Calcium that still resides in the water once normal pH levels are achieved tends to be calcium bicarbonate (Ca(HCO3)2), another soluble form of calcium.

Hollows in the Plaster

In spite of the best care a plasterer may take, there are times when cavities or voids are present in the plaster. These voids may be the result of shrinkage cracks, hollows between fixtures and plaster, or the lack of a good bond between the plaster and the underlying base material. (This lack of bond is referred to as delamination or bond failure). Delaminated areas can be small (2-3 inches in diameter) or very large (3-4 feet or more - see picture). If the void is never exposed to water, the sequence for creating a nodule stops. If, however, water can enter the void through a connecting path (usually either a crack or pinhole, depending on the shape of the delamination and the nature of the flexural force involved), the sequence continues. Depending on when the path is opened, voids in plaster may become filled with water as soon as the pool is filled, or they may not fill with water until months or years have passed. Voids may even develop after time, if delamination occurs due to ground shifting or other extraneous forces.

Regardless of whether the void is filled with water immediately or down the road, the process of hydration will occur inside the void just as it did out on the face of the pool when it was new. Only this time the calcium hydroxide is temporarily trapped, allowing it to concentrate - creating a strong, localized body of the material from which a nodule can be made. But it then travels out to the main body of water in the pool where it can react with alkalinity to transform into calcium carbonate. Where does this conversion to non-soluble calcium occur? In our plaster dust example, the conversion occurred uniformly over the entire surface of the plaster, resulting in a uniform fall-out of plaster dust throughout the pool. In the case of super-saturated calcium water oozing out of a pinhole, the conversion occurs just as it exits the void and enters the pool, i.e.: on the plaster surface of the pool.

How Fast Does It Squirt Out?

The answer to that question seems to determine whether or not a nodule forms. If the supersaturated water squirts out fast enough, a small amount of plaster dust will form beyond the exit hole, and will disperse into the pool water. This amount is little enough that it is not noticeable. If it oozes out very slowly, it may even solidify in the hole and plug it up. If the speed is just right (or wrong), it will form a nodule around the exit hole.

What about those who claim that "aggressive water" causes nodules?

It is instructive to consider the case of pools that have been acid washed or subjected to the acid start-up procedure. These pools often have had enough muriatic acid added to expose the plaster to a pH of 4.5 and alkalinity level of 0 for over a week. In both cases, the plaster has a better appearance afterward than before, yet the resultant surfaces do not have any greater propensity toward nodules following the acid wash.

What Can Be Done To Avoid Nodules?

The best methods to avoid nodules are nothing new: prepare the surface properly to insure a good bond, use the correct amount of each component of the plaster, mix and apply it correctly, and allow it to hydrate and cure normally. The critical failures include:

  • weak bonds between the plaster and the subsurface (which explains why nodules are more prevalent in replaster work)
  • Over-accelerated drying, resulting in excessive cracking of the plaster, allowing the pool plaster to become too dry
  • The pool not being filled with water for extended periods or hot periods
  • Ground shifting
  • Too slow of filling in a new plaster pool, resulting in shrinkage spike holes or other such "artificially created" cavities

    Surface preparation and compatibility of new coatings to existing surfaces is crucial to many other applications besides pool plaster. Anyone who has spent hours or days removing old varnish from furniture or old paint from the eaves of your house prior to repainting is familiar with the concept. Those who are even more familiar with surface preparation are those who have failed to properly prepare the surface, or to ensure compatibility of a new paint with the old.

    Bonding plaster to fresh gunite is rarely a problem because there is a chemical bond (where curing plaster chemically "locks on" to curing gunite) in addition to a mechanical bond (where the fresh plaster fills in the intentionally rough surface of the fresh gunite). The "new plaster to old plaster" and the "new plaster to old gunite" combinations are much more difficult. This is because in these situations no chemical bonding is likely, due to the fact that the old plaster or gunite is already thoroughly cured or hydrated. This fact has given birth to companies manufacturing, distributing, and instructing plasterers on the use of additional chemical bonding agents.

    How Can I Remove Existing Nodules?

    If there is not an excessive number of nodules, our experience is that the best way to treat a nodule is to let it exhaust itself normally. Just as plaster dust formation stops when the normal amount of calcium cures out of the surface, a nodule will cease growing when a proportional amount of calcium cures out of the void. A nodule can be scraped or sanded from the surface, and will only continue to reappear until all of the calcium from the source has been exhausted. Sometimes one removal will suffice, and other times it takes 2, 3, or more removals. The number of times it regrows and the size of the growth can be an indication of the amount of plaster surface inside the void.

    What If There Are Too Many?

    There comes a point when there are just too many nodules in certain pools, and more drastic action must be taken. These (rare) cases are usually the result of excessive cracking of the surface, or of extensive bond failure in the pool. When this happens the nodules are actually an indication of much more serious problems that would justify replastering the pool.

    Whose "Fault" Is It?

    One of the biggest stumbling blocks in the industry today is the finger pointing that is done in trying to assign blame. The fact of the matter is that, like many other phenomena that are common in cement applications, nodules are not always preventable. Good technique on the part of the plasterer, along with sound bonding principles will eliminate the vast majority of nodules, yet the appearance of a few is not unexpected (especially on replaster jobs) and are easily dealt with.

    Sidebar 1

    This phenomenon has variously been referred to as calcium growths, nodules or nodes, spores, and effervescence. Despite the term used, the result is the same: a localized, raised concentration of calcium carbonate, either in the classic "volcano" configuration or in the "stalactite" drip, emanating from a crack or a pinhole in the plaster.

    Sidebar 2

    The Effect of pH on Calcium

    Calcium in pools tends to differing forms depending of the pH of the water, as the chart illustrates:

    11 hydroxide (soluble)
    9 carbonate (non-soluble)
    7 bicarbonate (soluble)

    1. Under normal conditions, the plaster (white) is bonded to the gunite substrate (speckled), which in turn rests on dirt (tan). Calcium hydroxide bleed-off from the plaster surface dilutes into the pool water (blue) and is converted to both non-soluble calcium carbonate (plaster dust) and soluble calcium bicarbonate. Continuous "rinsing" of the hydroxide bleed-off by the circulating pool water, as well as normal pool maintenance (such as brushing), prevents a buildup of high pH material on the plaster surface.

    2. Sometimes, an air cavity can be formed between the gunite and the plaster. This is referred to as "delamination" and the cavity is referred to as a "void." As long as the void is not connected to the surface of the plaster, the fact that the void even exists may not be known. Unless the plaster completely breaks free from the surrounding plaster, creating what is referred to as a "pop-off," or unless the delamination is extensive, this is not considered by the plaster industry to be a defect.

    3. In some cases, however, the void is connected to the surface by a small pinhole or hairline crack. Pinholes and cracks are created from structural flexing of the delaminated plaster. The type and size of resulting hole or crack is dependent on numerous factors, including the size and shape of the delamination, the nature of the structural flex, the strength and thickness of the plaster over the delaminated section, etc.

    4. Gradually, water from the pool penetrates the void via the hole or crack, and creates a localized chemistry environment completely separate from the water balance in the pool. As calcium hydroxide bleeds into the void water it creates a calcium-rich, high pH solution like a little "calcium/pH factory" beneath the plaster surface. The pinhole or crack is not of sufficient size to create a rinsing effect like that going on at the plaster surface.

    5. Calcium-rich void water and bicarbonate-rich pool water, in contact with each other at the plaster surface, react with each other and seek equilibrium, which results in the production of an insoluble calcium carbonate by-product.

    6. If the conditions are right, this insoluble calcium carbonate can build up a "slag pile" around the exit point, thus forming a nodule.


    What's the difference between ammonia-based and copper-based algaecides?


    Algaecides, although not a necessity, can be a useful tool in the maintenance of an algae-free swimming pool. They do not replace the sanitizer (chlorine), but are like an "insurance policy" in that they can step in and inhibit algae growth even if the chlorine demand (amount of chlorine required to destroy algae, bacteria, and other contaminants in the pool) exceeds the amount of free available chlorine. The most common types of algaecides are the quaternary ammonium or "quat" algaecides and the metal algaecides (the most common of which contain copper).

    One of the problems with algaecides is that in too high of concentrations they can cause complications that you as a pool owner would prefer to avoid. Another problem is that, other than noting the amount you put in the pool, it is difficult to measure the actual level of algaecide in the water. Poolside test kits exist for some types of algaecides, but not for all - and those test kits that do exist can be awkward and time consuming to use.


    Quat algaecides have an attraction for the surface of algae plants, and can coat the plant sufficiently to suffocate it. The recommended dosage for most quat algaecides is 2.0 to 4.0 ppm.


  • It can be effective in controlling algae
  • It does not evaporate
  • It becomes more active when water temperatures increase
  • It concentrates on pool surfaces

    It affects the water surface tension, making it more difficult for chlorine to combine and stay in solution It has its own chlorine demand - meaning that there is an increase in the amount of chlorine required to maintain a residual when quat compounds are present. Over-dosing can cause excessive foaming, a soapy feeling, cloudiness, and a rapid loss of chlorine DE and sand filters absorb quats, increasing the need for careful and continuous maintenance dosing.


    Copper algaecides have been used since the early 1900s, and work by making it difficult for algae to eat or breathe.


  • It can be effective in controlling algae
  • It does not evaporate
  • It becomes more active when water temperatures increase
  • It concentrates on pool surfaces


    Although most modern copper-based algaecides contain a chelated form of copper which is less likely to deposit than normal copper in the water, over-dosing can cause blue-green copper sulfate staining of the plaster.

    Iron stains on plaster pools.

    Iron Stains

    One of the most common stains found in swimming pools and spas is from iron. Iron staining results from a depositing of ferrous oxide (rust) on the interior surfaces of the pool.

    The color of iron staining ranges from a light yellow to a darker brown color. The color intensity will vary depending on the amount of iron present, the source of the iron, and the type (color, porosity, etc.) of material it deposits on. The patterning of the deposits vary, but typically iron deposits preferentially concentrate:

  • Where the most porous plaster is in certain areas of the pool
  • Where there is the least amount of calcium deposited in the past
  • Where the greatest amount of calcium is depositing currently in the areas of the pool least affected by circulation
  • Where the brushing and/or automatic pool cleaner spends the least amount of time

    Unfortunately, this staining pattern is very similar to the patterning of dirt stains (i.e.: dirt that has sat on the same spot long enough to affect the coloration of the plaster, and to be fixed in place by calcification). The easiest way to distinguish between dirt stains and iron stains is to examine the plastic components of the pool: the return outlets in the pool, the inside of the skimmer, the plastic parts of an automatic pool cleaner, etc. Since iron has a greater affinity for plastic than for plaster, when iron staining is present there is almost always a brown film on the plastics. Dirt does not cause this phenomenon.

    There are many sources for iron in a swimming pool, the most common of which include source water provided by the water utility (the water used to "top off" the pool), galvanized or other iron-based pipe in the pool filtration system, galvanized or other iron-based pipe in the source water system, and spilled lawn and garden fertilizer with iron components.

    Contamination from source water and/or iron-containing home piping can be determined by lab analysis of the tap water used to fill the pool. Fertilizer contamination usually requires direct knowledge of the event by the person who applied the fertilizer. Iron contributed by the filtration system is usually detectable by examining the piping itself. The most common locations for this piping are either the pipe leading immediately into and out of the pump, and the pipe leading immediately into and out of a heater. If iron pipe is threaded directly into other metals (such as copper, bronze, or brass) then water flow over this join will form a mild electrical field and de-plate the galvanized pipe (which is the weaker of the two metals). It is common on older pools where galvanized pipe was used in conjunction with a bronze pump to be able to remove the hair/lint strainer (pump pot) lid and see iron corrosion in the galvanized nipple, which then "drips" into the pump cavity. This is why galvanized pipe is usually avoided in newer or more expensive pools.

    It is rare to actually get an iron reading in properly balanced pool water, since proper oxidation of water forces iron out of solution. Pools which are not regularly and properly chlorinated (including pools which only receive low-level chlorination through a feeder but no periodic "burning out" of contaminants) may contain dissolved iron, but this iron will deposit as soon as the first proper oxidation of the pool water occurs.

    Iron deposits may be removed in many different ways. Without draining the pool, there are chemical methods of stain removal which may or may not work depending on the severity and chemical composition of the stain. A topical application can tell you whether this method will work in your pool. The stains may also be removed by draining the pool and acid washing/sanding the pool. You would want to consult a professional plaster or service company for a consultation and estimate if this course is considered.

    Iron deposits may be avoided (or at least the rate of deposition may be slowed) by the use of a chelation/sequestering chemical. Your Pool Chlor service technician can provide you with further information about this product. Chelation/sequestering chemicals are also available at local retailers, usually labeled as "stain preventatives."


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