WATER QUALITY
The water numbers to hold, and how to move them
Hold pH at 7.2–7.6 and free chlorine at 1–3 ppm, and always correct total alkalinity first — until it is right, pH will not stay where you put it.
Balanced water is water that actually sanitises, does not sting eyes or skin, and neither corrodes the equipment nor scales it up. There are only five or six numbers, and because they push each other around you correct them in order rather than all at once.
| Reading | Hold it at | Move it with |
|---|---|---|
| Total alkalinity | 80–120 ppm | Sodium bicarbonate to raise, acid to lower |
| pH | 7.2–7.6 | Acid to lower, soda ash to raise |
| Free chlorine | 1–3 ppm | 65% granular chlorine, or the salt cell output |
| Cyanuric acid (stabiliser) | 30–50 ppm | Add stabiliser to raise; only partial draining lowers it |
| Calcium hardness | 200–400 ppm | Calcium chloride to raise; partial draining to lower |
| Salt (salt pools only) | 3,000–4,000 ppm | Pool-grade salt |
The order to work in
The order is not a convenience. Total alkalinity is the buffer that holds pH still — while it is low, pH swings on its own every day no matter how often you correct it — and chlorine only sanitises properly once pH is where it should be. So: alkalinity, then pH, then chlorine.
Take the sample from the middle of the pool at about elbow depth — not from the surface, and not next to a return.
Bring total alkalinity into 80–120 ppm first.
Wait 6 hours with the pump running.
Measure again and set pH to 7.2–7.6. Correcting the alkalinity usually carries it part of the way on its own.
Set free chlorine to 1–3 ppm last.
Add one product at a time, always dissolved in a bucket of water first, poured slowly around the pool with the pump running.
Leave at least 4 hours between one product and the next.
Re-test the next day. A reading taken straight after dosing is not the real number — the pool has not finished mixing.
How often to test
Chlorine and pH: twice a week, plus after any heavy rain or a busy weekend in the pool.
Total alkalinity: monthly.
Stabiliser and calcium hardness: every three months, and after any large top-up with fresh water.
Salt: monthly, on salt pools.
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