pools

Pool Chemistry

PH Concentration Level

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.  It is measured on a scale of 0 (strong acid) to 14 (strong base), with 7 being the neutral PH.  In pools, a lightly alkaline PH of 7.4 to 7.6 is desirable.  This range is the most comfortable to the human eye.  It also provides for optimum use of free chlorine while maintaining water that is not corrosive or scale-forming.

swimming pool
Effects of PH level
If PH is too low (below 7) If PH is too high (above 8)
  • 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
  • Chlorine activity is slowed and becomes inefficient
  • Scale formation in pipes occurs
  • Pool walls become discolored
  • Water becomes cloudy
  • Filter is overworked
  • Eye irritation may occur
Factors which affect PH
Lowers PH Raises PH
  • Acid
  • Gas Chlorine
  • Trichlor Chlorine
  • Dichlor Chlorine
  • Rain Water
  • Alum
  • Organic Litter
  • Make up Water
  • Soda Ash
  • Sodium Hypochlorite
  • Calcium Hypochlorite
  • Caustic Soda
  • Bicarbonate of Soda
  • Swimmer Wastes
  • Algae growth
  • Make up water

Raising PH with soda ash

 
If PH is under 7.4 - 7.6, add this amount of soda ash, then retest.
PH Gallons in Pool
1,000 5,000 10,000 15,000 20,000 25,000 50,000
7.2 - 7.4 1/24 lbs 1/12 kg 1/6 kg 1/4 kg 1/3 kg 1/2 kg 1 kg
7.0 - 7.2 1/20 lbs 1/8 kg 1/4 kg 1/3 kg 1/2 kg 2/3 kg 1 1/8 kg
6.6 - 7.0 1/12 lbs 1/6 kg 1/3 kg 1/2 kg 2/3 kg 1 kg 2 kg
Under 6.7 1/8 lbs 1/4 kg 1/2 kg 2/3 kg 1 kg 1 1/8 kg 2 1/4 kg

PH is lowered by adding dry acid (sodium bicarbonate) or muriatic acid (HCL).  Use of dry acid is safer than muriatic acid.  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 acid to the water” (never add water to acid).

Lowering PH with dry acid / sodium bicarbonate

 
If PH is over 7.6, add this amount of acid, then retest.
PH Gallons in Pool
1,000 5,000 10,000 15,000 20,000 25,000 50,000
7.6 - 7.8 1 1/4 oz 6 oz 1/12 gal 1/8 gal 1/6 gal 1/4 gal 1/2 gal
7.8 - 8.0 1 1/2 oz 8 oz 1/8 gal 1/6 gal 1/4 gal 1/3 gal 5/8 gal
8.0 - 8.4 2 1/2 oz 1/12 gal 1/6 gal 1/3 gal 3/8 gal 1/2 gal 1 gal
Over 8.4 3 oz 1/8 gal 1/4 gal 1/3 gal 1/2 gal 5/8 gal 1 1/4 gal

 
If PH is over 7.6, add this amount of dry acid, then retest.
If PH reading is Add for each 10,000 gallons of pool water
7.2 - 7.6 Do not add
7.7 - 8 3/4 lb
8.1 - 8.4 1-1/4 lb
Above 8.4 1-1/2 lb

Lowering PH with muriatic acid