How to balance pool water chemistry

Chemistry is the job. Get the order right and a pool holds itself between visits; get it wrong and you're chasing algae, burning chlorine and eating the cost. Here are the ranges pros hold and the sequence they adjust in.

A field guide for pool service techs and owner-operators.

Almost every "problem pool" on a route is a chemistry problem wearing a costume. Cloudy water, scale on the tile, a chlorine bill that won't quit, a heater that failed early — trace them back and you'll usually find alkalinity that was never corrected or cyanuric acid nobody tested. Balancing water isn't complicated, but it is ordered, and doing it out of order means doing it twice.

The target ranges

The order to adjust in

1. Total alkalinity

TA is the shock absorber. Below about 80 ppm, pH swings wildly on every rain and every gallon of acid; above 120 ppm, pH creeps up relentlessly and you're adding acid every week. Raise TA with sodium bicarbonate; lower it by adding acid slowly, ideally in a column poured into a still spot rather than broadcast across the surface.

2. pH

Hold 7.4–7.6. Chlorine's killing power falls off a cliff as pH climbs — at 8.0 a large share of your chlorine is doing nothing, which is why "the pool needs more chlorine" is often really "the pool needs acid." Muriatic acid or dry acid brings it down; soda ash brings it up.

3. Calcium hardness

Aim for 200–400 ppm (higher end on plaster, lower on vinyl and fiberglass). Soft water is aggressive — it pulls calcium out of plaster and grout. Hard water scales tile, heater exchangers and salt cells, and there's no chemical that removes calcium: the only fix is dilution or a partial drain and refill, so price that job accordingly.

4. Cyanuric acid

This is the reading most routes ignore and the one that quietly costs the most money. Without CYA, sunlight destroys unstabilized chlorine within hours. With too much of it — the inevitable result of running trichlor tabs all season — chlorine gets locked up and stops sanitizing even when the test says it's present, and the customer's pool goes green while your test kit says 3 ppm. Rule of thumb: free chlorine should be roughly 7.5% of the CYA level. There's no chemical that reduces CYA either — it's dilution. Test it at least seasonally on every pool.

5. Sanitizer

Only after the rest is in range should you set chlorine. Liquid chlorine (no CYA added), cal-hypo (adds calcium), trichlor tabs (adds CYA), or a salt cell — every choice moves another reading, which is why sanitizer comes last.

Reading a pool without a test kit

You still test, but a good tech diagnoses from the deck on the walk-up: scale on the waterline (high pH/calcium), a rough plaster feel (aggressive water), a heater that short-cycles (scale), rapid chlorine loss with clear water (CYA or a chlorine demand), cloudy water with normal chlorine (filtration, high pH, or high CYA). The kit confirms what your eyes already suggested.

Log every reading — that's the real product

Chemistry only makes sense as a time series. One reading is a snapshot; twelve weekly readings tell you the pool's chlorine demand, whether the CYA is climbing, and whether that "sudden" green pool was actually two months of drifting alkalinity. It also settles disputes instantly — a dated log with a photo is the difference between "you let my pool go green" and a client who can see exactly what happened while they were on vacation.