It is important that you understand the role of the various chemicals used to keep pools clean. Basically, if the water in the pool is clear and blue, the following three conditions should be satisfied:
- The acidity-alkalinity balance is correct,
- All algae and bacteria have been eliminated, and
- All suspended solids have been removed.
The object of treating the pool water is to maintain these balances. If any of them is allowed to get out of control then the water in the pool will not be sparkling blue.
Acidity-Alkalinity (pH)
The balance between the acid and the alkalines in a pool is measured on the pH scale, which can vary between 1 and 14. Distilled water has a pH of 7.0 (neutral) and the ideal pH for pool water is between 7.2 and 7.6. If it is allowed to go higher than this (too alkaline) the water may become cloudy and the effectiveness of chlorine to kill bacteria and algae will be reduced. If the pH drops below 7.0 (too acid) then steel fittings will start to corrode and the water will irritate swimmers' eyes. The effectiveness of chlorine will also be diminished. pH can be easily measured using a test kit, which has a colour-coded comparator for easy reading. When a pool is first filled the pH should be tested daily until a consistent reading is obtained. There after testing need only be done once a week or even less frequently if the water remains clear and blue.
pH too high (above 7.6)
If the pH is too high it must be lowered by the addition of acid. The acid can either be in granular or liquid orm and is marketed as “HIGH PH” or “pH MINUS". The dosage rates to reduce the pH will be indicated on the package.
For liquid acid approximately 60 cc (gms) of acid will be required for each 0.1 reduction in pH for each 10,000 litres (10m3) of water.
After adding acid the water should be allowed to circulate for four hours before testing again. If the pH is still too high then the procedure outlined above should be repeated.
pH too low (below 7.2)
If the pH is too low it must be raised by the addition of soda ash (sodium carbonate) which is marketed as “LOW PH” or “PH PLUS”. The procedure is the same as outlined above for reducing the pH but the dosage rate is 50 gms per 0.1 increase in pH per 10,000 litres.
As soda ash is a powder it is best to pre-mix it with water before pouring the concentrated solution into the pool.
The checking and re-application procedure is as for high pH.