How to balance pool water

Every adjustment starts with a reading. Use fresh test strips, a liquid test kit, or a digital meter, and test at least weekly — more in peak season or heavy use. Record the numbers so you can see trends, not just snapshots. Adjust one thing at a time and re-test before the next change; chemistry is interconnected, and chasing several numbers at once is how pools end up worse than they started.

Alkalinity is your buffer — it keeps pH from bouncing around. Balance it before pH, because alkalinity strongly influences where pH settles. Low alkalinity makes pH unstable and water corrosive; raise it with sodium bicarbonate (baking soda). High alkalinity drives pH up and clouds water; lower it with acid added slowly, in stages.

pH affects swimmer comfort and how effectively chlorine sanitizes. Below 7.2, water turns aggressive and eyes sting; above 7.8, chlorine loses punch and scale forms. With alkalinity already in range, nudge pH into the 7.4–7.6 window and re-test.

Calcium protects plaster, grout, and metal. Too little and water pulls calcium out of surfaces (etching, pitting); too much and it deposits as scale. Raise hardness with calcium chloride. The only practical way down is to dilute with fresh water — which is why knowing your pool volume matters before you drain and refill.

Cyanuric acid (CYA, or stabilizer) shields chlorine from sunlight — without it, UV burns off your sanitizer in hours. But there's a catch: the more CYA you have, the more free chlorine you need to stay effective. Keep CYA around 30–50 ppm for traditional pools (higher for saltwater), and scale your chlorine target to it. The only way to lower CYA is dilution.

Salt chlorine generators need salinity in a specific band — commonly 2,700–3,400 ppm, but always confirm your chlorinator's target. Too low and the cell can't produce chlorine; too high and you risk corrosion and error codes. To raise it, add pool-grade salt in stages and re-test as it dissolves. Our salt calculator tells you how many pounds (and bags) to add for your volume.

Individual readings can each look fine while the water as a whole still drifts corrosive or scaling — because temperature, pH, calcium, and alkalinity interact. The Langelier Saturation Index (LSI) rolls them into one number: below −0.3 is corrosive, above +0.3 is scaling, and −0.3 to +0.3 is balanced. Because it depends on temperature, the same water can drift across seasons, which is why pros check it on every visit. Run your numbers through the LSI calculator to confirm the whole picture is in range.

Chemistry only works if the water moves. The pump should circulate the entire pool — one “turnover” — once or twice a day so chemicals distribute and the filter does its job. Use the pump run-time calculator to set a daily schedule from your volume and pump flow rate, and run longer in hot weather or when clearing a problem.