CHLORINE LEVEL PROBLEMS
Chlorine has been added, but there is no reading on the test kit.
Caused by: Chlorine level is high and bleaches the test kit colouring agent. To confirm, see if you can smell chlorine at the surface, or repeat the test with only a droplet of pool water in the test tube and watch closely to see if there is a discolouration before the bleaching occurs.
Cure: Determine the approx level of chlorine by diluting the sample of pool water with an equal quantity of distilled water; multiply the result by 2. If there is still no reading, repeat the process and multiply the answer by 4...and so on. Alternatively, use an electronic meter to test the chlorine level.
If the actual chlorine reading is below 10ppm suspend dosing and allow it to drop over time. If higher, or you need to use the pool soon, add sodium thiosulphate to reduce free chlorine. WARNING The dose rate is 250 grams per 50 cubic metres. Apply in several smaller additions, testing after each dose. If overdosed, sodium thiosulphate can give you a chlorine deficit for weeks.
Difficult to maintain chlorine level.
1st suspect - Free chlorine is being decomposed by UV from the sun.
Cure: For pools using liquid chlorine (sodium hypochlorite) or calcium hypochlorite, add stabiliser (cyanuric acid) at a rate of 500 grams per 50 cu metres. Dose directly into the pool, NEVER pre-mixed with the chlorine. Alternatively, switch to stabilised chlorine - dichlor or trichlor in granules or tablet form.
2nd suspect - High water temperature. Bugs prefer warm water and breed quickly - more bugs create a higher chlorine demand. As a rough rule of thumb - if the pool water temperature goes above 26 degrees C, the chlorine demand will double for every 5 degrees.
Cure: Increase the dose rate of chlorine proportionately.
3rd suspect - Chlorine levels have been low, there has been a build-up of pollutants, and therefore an increase in chlorine demand. Cure: Superchlorinate to 10ppm free chlorine.

WATER BALANCE PROBLEMS
pH remains below 7.2.
Likely cause: Usually due either to low pH of mains water (soft water areas) or to the use of an acidic chlorine donor, such as trichlor. Cure: Correct the pH.
Consider changing to a high pH chlorine source to help achieve a natural balance between the low pH of the incoming water and the high pH of the chlorine donor. Trichlor is low pH, Dichlor is roughly pH neutral; calcium hypochlorite and sodium hypochlorite are high pH chlorine donors.
Tendency for the pH to be permanently high (above 7.6).
Likely cause: This is due to either (1) high pH of mains water (hard water areas) or (2) the use of alkaline chlorine donors such as calcium or sodium hypochlorite, or (3) hardness salts being leached from new concrete or mosaic pools. Cure: The remedy is the same whichever factor is at work here - correct the pH. For (1) or (2), consider changing to a low pH chlorine donor to help achieve a natural balance between the high pH of the water and the low pH of the donor. Trichlor is the obvious chlorine donor to choose. For (3), the difficulties with new pools will clear up of their own accord given sufficient time.
pH values are erratic and fluctuate. Likely cause: Total Alkalinity is too low to buffer the pH.
Cure: Add sodium bicarbonate to ensure total alkalinity remains above 100ppm. The dose rate is 1.5kg per 50 cu metres of pool water.
pH is locked.
Likely cause: The water is over buffered due to high alkalinity. This is a not uncommon problem in hard water areas where the mains feed water has a high total alkalinity.
Cure: Add dry acid (Sodium bisulphate) to lower the total alkalinity to below 200ppm. The dose rate is 1kg per 50 cu metres of pool water. Add the acid a little at a time, pre-dissolved at a dilution no stronger than 8:1.
Tendency towards low alkalinity.
Likely cause: The local feed water is low in bicarbonates and, whenever the pool is topped up, bicarbonates in the pool are diluted. This is a particular problem in soft water areas.
Cure: Add sodium bicarbonate to raise total alkalinity to around 100ppm. A dose of 1.5kg per 50 cu m of pool water should raise the level by 20ppm.

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Deep Blue Pools, Alhaurin el Grande, 952 594 393
Copyright Ken Walker, Deep Blue Pools, July 2006