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.
| If PH is too low (below 7) | If PH is too high (above 8) |
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| Lowers PH | Raises PH |
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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