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Pool Chemistry

 

Essentials of Pool Chemistry and Maintenance
Chemical Factor
Swimming PoolsDrinking Water
Free chlorine residual (chlorine and hypochlorites)0.3 to 0.7 ppm0.2 to 0.6 ppm
PH concentration7.2 to 7.67.2 to 8.0

 

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.

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 PHRaises 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.
PHGallons in Pool
1,0005,00010,00015,00020,00025,00050,000
7.2 - 7.41/24 lbs1/12 kg1/6 kg1/4 kg1/3 kg1/2 kg1 kg
7.0 - 7.21/20 lbs1/8 kg1/4 kg1/3 kg1/2 kg2/3 kg1 1/8 kg
6.6 - 7.01/12 lbs1/6 kg1/3 kg1/2 kg2/3 kg1 kg2 kg
Under 6.71/8 lbs1/4 kg1/2 kg2/3 kg1 kg1 1/8 kg2 1/4 kg

PH is lowered by adding muriatic acid (HCL).  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 muriatic acid

If PH is over 7.6, add this amount of acid, then retest.
PHGallons in Pool
1,0005,00010,00015,00020,00025,00050,000
7.6 - 7.81 1/4 oz6 oz1/12 gal1/8 gal1/6 gal1/4 gal1/2 gal
7.8 - 8.01 1/2 oz8 oz1/8 gal1/6 gal1/4 gal1/3 gal5/8 gal
8.0 - 8.42 1/2 oz1/12 gal1/6 gal1/3 gal3/8 gal1/2 gal1 gal
Over 8.43 oz1/8 gal1/4 gal1/3 gal1/2 gal5/8 gal1 1/4 gal

 

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