Chemicals used in Swimming Pools:
Proper water chemistry is essential to maintaining safe and consistent swimming pool operation. Chemicals used in swimming pools include: Disinfectants to destroy harmful or otherwise objectionable organisms; Alkalinity and pH Adjusters to maintain a consistent acid-base relationship and acid buffering capacity; Chlorine Stabilizer to prevent unnecessary loss of chlorine; Algicide to kill and prevent algae, and Filter Aids to help remove foreign material. Following is a discussion of various factors which affect water chemistry, how they affect swimming pools and how to use pool chemicals to restore a properly balanced water chemistry.


pH is the single most important element in swimming pool water chemistry. It affects every other chemical balance in pool water.

pH is a measure of hydrogen ion (H+) concentration in water. It indicates the relative acidity or basicity of pool water. pH is measured on a scale of 0 (strong acid) to 14 (strong base) with 7 being the neutral pH.

In pools a slightly alkaline pH of 7.4 to 7.6 is most desirable because this range is most comfortable to the human eye and provides for optimum use of free chlorine while maintaining water that is not corrosive or scale forming.

If pH is too low (below 7)

  • Water becomes acidic
  • Chlorine residuals dissipate rapidly
  • Eye irritation occurs
  • Plaster walls are etched
  • Metal fittings, pump impeller, heater core may corrode
  • Dissolved metals may leave stains on walls
  • Rapid Loss of alkalinity

If pH is too high (above 8)

  • Chlorine activity is slowed and inefficient
  • Scale formation and discoloration of pool walls
  • Water becomes cloudy
  • Filter is overworked
  • Eye irritation may occur

pH Adjustment
To avoid the problems listed above, pH must be maintained between 7.2 and 7.8. The most desirable level for pH is between 7.4 and 7.6. If pH is too low – run alkali demand test if available. Raise pH by adding soda ash (sodium carbonate). Never add more than 2 lbs per 10,000 gallons in a single treatment. Be sure the pump is running when chemicals are added. Allow to recirculate then retest to determine if further treatment is necessary. Caustic soda (sodium hydroxide) is sometimes used with chemical feed pumps to raise pH. If problems with low pH persist, it may be necessary to raise total alkalinity to stabilize the pH.

Chart No. 1 – Raising pH with Soda Ash
(If pH is under 7.4, add this amount of soda ash, then retest)

pH 1,000 5,000 10,000 15,000 20,000 25,000 50,000
7.2-7.4 2/3 oz. 3 oz. 6 oz. 9 oz. 12 oz. 1 lb. 2 lbs.
7.0-7.2 3/4 oz. 4 oz. 8 oz. 12 oz. 1 lb. 1 1/4 lbs. 2 1/2 lbs.
6.6-7.0 1 1/4 oz. 6 oz. 12 oz. 1 lb. 1 1/2 lbs. 2 lbs. 4 lbs.
Under 6.7 1 1/2 oz. 8 oz. 1 lb. 1 1/2 lbs. 2 lbs. 2 1/2 lbs 5 lbs

If pH is too high – run acid demand test if available. pH is lowered by adding muriatic acid (hydrochloric acid) or sodium bisulfate. Carefully add acid at the deep end of the pool. Try not to pour acid near pool walls or fittings. Remember: When using or diluting acids,” do as you oughta, add the acid to the water” (never add water to acid)
NOTE: 10 lbs sodium bisulfate is roughly the same as 1 gal muriatic acid.

Chart No. 2 – Lowering pH with Muriatic Acid
(If pH is over 7.6, add this amount of acid, then retest)

pH 1,000 5,000 10,000 15,000 20,000 25,000 50,000
7.6-7.8 1 1/4 oz. 6 oz. 12 oz. 18 oz. 24 oz. 1 qt. 2 qts.
7.8-8.0 1 1/2 oz. 8 oz. 16 oz. 24 oz. 1 qt. 1 1/4 qts. 2 1/2 qts.
8.0-8.4 2 1/2 oz. 12 oz. 24 oz. 1 1/4 qts. 1 1/2 qts. 2 qts. 1 gal.
Over 8.4 3 oz. 16 oz. 1 qt. 1 1/4 qts. 2 qts. 2 1/2 qts. 1 1/4 gal.
Factors which affect pH:
Lowers pH Raises pH
Acid Soda Ash
Gas Chlorine Sodium Hypochlorite
Trichlor Chlorine Calcium Hypochlorite
Dichlor Chorine Caustic Soda
Rain Water Bicarbonate of Soda
Alum Swimmer Wastes
Organic Litter Algae Growth
Make up Water Make up Water

About Red Square Pools

Thank you for checking out our blog...we appreciate you taking the time to read our posts. To be quite honest, our posts come from your questions. Red Square Pool's wants to clear up the confusion and frustration of maintaining your pool and spa. We simply want to make Pool Maintenance and Repair SIMPLIFIED!! Let us know what your thinking by dropping us an email at info@redsquarepools.com. Have a safe and happy swimming experience!

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