about products maintenance troubleshooting safety tips glossary contact

American Pool Supply
[ a ] [ b ] [ c ] [ d-f ] [ g-l ] [ m-o ] [ p-q ] [ r ]
[ s ] [ t-v ] [ w-z ]



A chemical which lowers pH when added to water. Sodium bisulfate (dry acid) is a very strong acid.

Acid Demand

The amount of acid necessary to lower the pH to the proper range (7.4 to 7.6). When your pool is over-alkaline it "demands" acid. How much acid you should add can be deter mined with a DPD Test Kit from American Pool Supply.

There are two important facts to remember when performing the acid demand test. FIRST, in order to get the most accurate readings, it is important that you swirl the water sample rather than shake it. SECOND, when you are unsure of the amount of water your pool contains, you should determine the amount of acid needed for the smallest gallonage possible to avoid the addition of too much acid.

If you do not have a test kit that measures acid demand and your pH is high, you should add no more than an 8 oz. cup of muriatic acid per 20,000 gallons of water at one time, checking in about six hours to see if more acid is needed. Repeat this procedure until pH is in the proper range.

Any acid should be diluted by adding the acid to a plastic pail of water (not the reverse). With pump on, add acid to the pool slowly, about 18 inches from the sides of the pool, pouring the acid into the stream of water returning from the filter. Avoid area of the surface skimmer or any metal fixture. If the test for acid demand indicates a large amount of acid, do not add more than one quart per 20,000 gallons at one time. Allow about six hours between additions.

With small spa pools, the recirculation pump should be turned off before acid is added and the aeration pump should be left on. Dry acid is recommended for spas.

top Algae

Algae is a simple plant type growth that forms in the pool water or on the walls, in the corners and on the floor of the pool. It can cause clogged equipment, slippery surfaces, green water and increased chemical use. Algae is usually green, black (spots), yellow or yellow-orange to red-orange in appearance.

Add a 60% algaecide as a supplement to regular chlorination for algae prevention. If algae already has started to develop, particularly the attached dark green (black) or yellowish (mustard) algae, it should be destroyed as quickly as possible because the longer it is allowed to remain, the more difficult it is to remove.

  1. First add the algaecide to the pool following the instructions on the label.
  2. The algae spots should be brushed thoroughly to remove most of the raised portion of the algae. Be sure to remove algae forms as a mat around the light rim or where the ladded attaches to the pool. If necessary, use a stainless steel brush (only on plaster pools).
  3. Adjust the pH to about 7.4 using the acid demand test in your test kit.
  4. The next day after adding the algaecide, give the pool a double superchlorination with one gallon of liquid chlorine per 10,000 gallons.

Brush all remaining spots again. Allow the filter to run continuously about 3-4 days and keep free chlorine residual up to about 2.0 PPM. Examine any refill water pipes to be sure there is no algae present to reinfect the pool. Clean your brush with strong bleach solution to kill algae cells clinging to the fibers. Do not resume swimming until chlorine residual drops to 2.0 PPM or less.


A chemical used to kill existing algae or prevent the growth of algae.

top Bacteria

Very small organisms continuously entering the water via swimmers, dust, etc. Without proper sanitation, pools are a perfect breeding ground for bacteria, many of which can cause decease and/or infection.

Balanced Water

Water which has the correct values of pH, alkalinity, and calcium hardness. Water out of balance can cause corrosion or scaling.


A chemical which raises pH when added to water. Sodium carbonate (soda ash) is a very strong base.

Bather Load

The number of individuals using a pool in a 24 hour period and the pool's principal source of bacterial and organic contamination.


A chemical element that exists as a liquid in its elemental form or a part of a chemical compound which is a strong oxidizer and sanitizer.

top Bromamine (Combined Bromine)

A group of bromine-ammonia compounds formed when bromine combines with organic wastes in the water. Unlike chloramines, bromamines are effective sanitizers and are not smelly or irritating to the eyes.


A dispensing device for feeding brominating tablets into pool's recirculating system

Bromine Demand

The amount of active bromine required to destroy and oxidize bacteria, algae and organic swimmer waste. When the "demand" is satisfied the water is considered safe to use.


A chemical which helps water resist pH change.

top Calcium Hardness

The amount of calcium dissolved in water. The correct range for pools is 150-300 ppm. High levels promote scale and cloudy water. Low levels cause corrosion of pool equipment.


A group of chlorine-ammonia containing compounds formed when chlorine combines with organic wastes in the water. Chloramines are not effective as sanitizers and are responsible for eye and skin irritation, as well as pungent odors.


A commonly used bacteria-killing agent used both as an oxidizer and sanitizer.

top Chloramine (Combined Chlorine) A compound formed when chlorine combines with nitrogen or ammonia which causes eye and skin irritation and has a strong objectionable odor.

Chlorine Demand

The chlorine necessary to destroy and oxidize bacteria, algae and other organic wastes.

Chlorine Residual

Also called free or available chlorine. The amount of chlorine available for sanitation after the chlorine demand has been met.


A chemical which, when present in pool water at proper levels, reduces loss of chlorine due to sunlight.


The removal of metal from copper or other metal surfaces in a destructive manner. corrosion is caused by improperly balanced water or excessive water velocity through piping or heat exchangers.

top DPD The reagent used in test kits to indicate free available chlorine or bromine. DPD turns pink when chlorine or bromine are present. DPD is recommended for chlorine testing. (See OTO)


To Kill and inhibit growth of harmful bacteria and virus in pool water.

Dry Acid

A granular chemical used to lower pH and/or total alkalinity.


A device that removes undissolved waste particles from the water by recirculating the water through a porous substance, a filter medium or element.

Free Available Chlorine (Chlorine Residual)

That potion of the total chlorine remaining in chlorinated water that is not combined with ammonia or nitrogen compounds and will react chemically with undesirable or pathogenic organisms.

top High Total Alkalinity

In many parts of the United States the alkalinity of the water is high (in some cases, as much as 300-400 PPM) and as a result, the pH of the water tends to remain high (8.2-8.4).

Acid should be added to lower the pH to the desired 7.4-7.6 range. The acid will also destroy a small amount of the alkalinity. However, within the next 2 to 4 hours, the pH generally bounces back to above 8.0 because of the high remaining total alkalinity reserve still remaining in the water. Although high total alkalinity indicates there will be a frequent need for acid, never add acid to the pool without first checking the pH and acid demand.

Only by frequent adjustments of pH with acid will alkalinity eventually be lowered to the proper level. At this point, pH will be more or less "stabilized" and will tned to rise at a lower rate. Acid then will be needed less frequently and in smaller amounts.

Low Alkalinity

If you live in an area where the alkalinity of the water is abnormally low, the water tends to be corrosive to the finish of plaster pools. Often pH is too easily lowered below 7.0 and this may result in corrosion of the metal equipment and plumbing, wrinkling of vinyl liners and severe eye irritation. If pH and total alkalinity are both low, first increase the total alka linity to the proper range. Usually this adjustment also brings the pH up to the proper level.

In some areas, pool water has a high pH even though total alkalinity is low. Under these conditions, you should adjust alkalinity first and then adjust pH. Otherwise, it is difficult to get pH in the proper range without going over acid.

You can increase alkalinity to the desired 100-125 PPM range with the use of alkalinity increaser. For every 1.5 pounds of alkalinity increaser to 10,000 gallons of water, alkalinity is raised 10 PPM.

top Non-chlorine Shock

An oxygen based shocking compound. Some non-chlorine shock compounds are fast dissolving and can allow swimming just 15 minutes after use.

Organic Wastes

Wastes such as saliva, urine, perspiration, and suntan oils which swimmers introduce into the pool. Most organic wastes will not filter out and must be removed by shocking.


A chemical reagent which reacts with total bromine or chlorine and turns yellow. OTO test kits don't easily indicate whether the chlorine or bromine is combined (as chloramines or bromamines) or available. OTO is acceptable for testing bromine, since bromamines are effective sanitizers, but DPD is recommended for chlorine (See DPD)

top pH Control

The term "pH" refers to the acid-alkaline balance of water expressed on a numerical scale from 0 to 14. A test kit measuring pH balance of your pool water is available from American Pool Supply. The control of pH is dependent to a large extent upon the total alkalinity content of the pool water.

Rule: 7.4 to 7.6 is a desirable pH range.

It is essential to maintain the correct pH. If pH becomes too high (over alkaline), it has effects:

  1. Greatly lowers the effect of chlorine to destroy bacteria and algae.
  2. Water becomes cloudy.
  3. There is more danger of scale formation, on the plaster or in the coils of the heater.
  4. Filter may become blocked.

If pH is too low (over acid), there may be:

  1. Excessive eye burn or skin irritation.
  2. Etching of the plaster.
  3. Corrosion of metal fixtures in the filtration and recirculation system which may create brown, blue, green or sometimes almost black stinas on the plaster.
  4. It destroys the chlorine very rapidly.

*Caution: Do not test for pH without first neutralizing the chlorine in the water sample.Otherwise, the chlorine may interfere with the test to give you a false reading. The DPD Test Kits containing neutralizer will enable you to check pH in the presence of a chlorine residual.

   6.8 7.0       7.2     7.4 7.6    7.8    8.0 8.2 8.4
Add Soda Ash...Marginal...Ideal...Marginal...Add Acid...

If your pool water pH is less than 7.2, turn off the pool, recirculation pump temporarily in order to minimize corrosion in your pool pump, heater, plumbing, etc. Add soda ash as a quick and simple way to bring the pool water pH back to a safe range. Remember to turn pool pump back on as you add the stabilizer. Maintain a normal chlorine residual, but do not super chlorinate for 4-5 days. Check the total alkalinity. If it is low, add sufficient alkalinity increaser to raise total alkalinity to the proper range and to prevent future low pH problems.

top Phenol Red A test kit chemical used to measure pH. High bromine concentrations can cause phenol red to turn purple (instead of red) which leads to a false high pH reading. If in doubt about your test kit, consult your dealer.


Parts per million. A concentration unit used to indicate the trace presence of various chemicals (hardness, sanitizer, or total alkalinity) in pool water. One ppm is the same as one ounce in 7.812 gallons (or 1,000,000 ounces).

top Reagents

Standardized chemical used to test various aspects of pool water (pH, bromine/chlorine levels etc.).

top Sanitize

To kill undesirable or pathogenic (disease causing) organisms, and having a measurable residual at a level adequate to maintain the desired kill.


A chemical which disinfects (kills bacteria), kills algae and oxidizes organic matter.

Saturation Index

An equation which uses water temperature, pH , total alkalinity, and calcium hardness to predict if the water is corrosive or scale forming. The saturation index gives a clear picture of your pool's water balance.

top Scale

In hardwater areas, pool water has a high calcium content, so it is necessary to control the pH and the total alkalinity carefully to prevent scale from forming. Scale is caused by deposits of calcium salts (usually calcium carbonate) and appears at the tile or water line, or the coil of the heater or, in a plaster pool, it may form either as sharp raised points or a discolored massive scale on the plaster surface.

Scale is often brownish in color due to entrapped dirt or iron present in the water. Calcium deposits can also form in the filter resulting in a rapid pressure build-up even if the filter has just been backwashed.

The calcium content and total hardness content of the pool increases due to repeated evaporation of the pool water and addition of refill water. The evaporation rate is increased by high water temperature and wind. After a period of time it may be necessary to drain the pool and refill it with fresh water.

It is a good policy to check your pool water for total hardness about 2-3 times a month with a Water Hardness Test Kit. Monthly tests are advisable for the spa (therapy) pools. The use of Scale and Stain control can help prevent or delay scaling.

Shock (Also known as superchlorination)

Ridding a pool of organic waste (through oxidation) by the addition of significant quantities of a sanitizer.

top Total Alkalinity

Total alkalinity is a measurement of the total amount of alkaline chemicals in the water and controls pH to a great degree. You can think of it as an alkaline reserve which will tell you whether or not your pool is in proper balance. It is not the same as pH which refers merely to the reltive alkalinity-acidity balance. Your pool water's total alkalinity should be in the 100-125 PPM range for easier pH control.

A total alkalinity test is simple to perform, with a test kit. You should test about 3 times a week to be sure it is being maintained. NOTE: If stain and scale prevention chemicals have been or are being used in the pool, keep total alkalinity about 20 PPM higher than normal.

Total Bromine

The sum of both the free available bromine and combined bromine.

Total Chlorine

The sum of both the free available chlorine and combined chlorine.

top Water Hardness

Water hardness is a measurement of the amount of calcium and magnesium in your pool. Generally about 70-75% of the total hardness of the pool water is calcium. Too much calcium is undesirable because it can cause the formation of calcium scale on the plaster finish or in the coils of a heater and block the filter.

The amount of water hardness tends to increase in a pool due to evaporation and addition of refill water. The use of calcium hypochlorite also increases the water hardness. Generally when the water hardness reaches a level of 400 ppm, the pool should be drained and refilled with fresh water. If the pool cannot be drained conveniently, use Stain and Scale Control to prevent or delay scaling.

Completely soft water with no hardness is undesirable in a pool because the water tends to be corrosive. Increase it by the addition of calcium chloride dihydrate. Every 1.25 lb. of this material added to 10,000 gallons of water will increase the hardness 10 PPM. This material is weakly acidic, so you should predissolve it in water before adding it to the pool and check pool pH one hour after making the addition.

If water used to fill a pool has an excessive hardness value, it may be desirable to pass 70-80% of the water through a softener before adding it to the pool. However, do not totally soften pool water.

The water hardness test kit will enable you to determine the amout of hardness in your pool water and your tap water in just a few minutes. The water hardness test should be performed every 3 months. ** Calcium Hardness in a plastered pool should be minimum of 200 PPM and no more than 350 PPM. Vinyl and Fiberglass, painted pools 175 PPM and no more than 275 PPM.

American Pool Supply
Contractors Number: AMERIPS111D1
Phone:1-800-628-7665 or 425-485-7676
Fax: 1-800-201-5511 or 360-668-6533

[Home] [About] [Products] [Maintenance] [Troubleshooting]
[Safety Tips] [Contact]


The contents of this web site are the property of American Pool Supply.
Copyright© 1997 - 2009 American Pool Supply
Web site by Net-Time