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Testing & Chemistry

Testing & Chemistry

Every dose on this site starts here, because every dose starts with a number you measured rather than one you assumed.

By Scooter M.Last reviewed September 2, 2026How we work the numbers out
Pool water testing equipment and reagent bottles at the poolside

The six numbers

What to measure, what to aim for, and where the target comes from
ReadingTargetSource of the targetWhat goes wrong outside it
Free chlorine1-4 ppm for routine sanitizingHTH states 1-4 ppm for its 3 inch tabs; the label is the binding authority under EPA FIFRABelow: algae. Above the label limit: not permitted, and irritating
pH7.2-7.6HTH pH Down product pageHigh blunts chlorine and clouds water. Low corrodes surfaces and metal
Total alkalinity80-120 ppmHTH Alkalinity Up product pageLow means pH bounces. High means pH will not move
Cyanuric acid30-50 ppm on tablet pools, 60-80 ppm saltwaterHTH Chlorine Stabilizer product pageLow: chlorine burns off in sunlight. High: chlorine stops working at any reading
Calcium hardnessRoughly 200-400 ppmGeneral industry practice; we could not source a manufacturer figureLow is corrosive. High scales and clouds
PhosphateBelow 200-500 ppbHTH Phosphate Remover product pageAbove it, algae becomes harder to control

Correct them in this order

  1. **Total alkalinity first.** It is the buffer that holds pH steady. Correcting pH on a pool with low alkalinity means correcting it again next week.
  2. **pH second.** Into the 7.2 to 7.6 range. HTH's own guidance is to wait four to six hours after shocking before adding acid.
  3. **Cyanuric acid third**, if it needs it. It dissolves slowly, so wait 24 to 48 hours before a retest means anything.
  4. **Chlorine last.** Because how much chlorine you need depends on all three of the readings above.
  5. **Calcium hardness and phosphate** as periodic checks rather than weekly ones. Neither changes quickly.

Why we show the arithmetic

Because the shorthand everyone repeats is only true for one pool and one product. 'One pound per 10,000 gallons' assumes a specific available-chlorine percentage; '1.4 lb of bicarb raises alkalinity 10 ppm' assumes 10,000 gallons. Change either assumption and the number is wrong.

Every dose table on this site is computed from the percentage printed on your product and the weight of water, and every one shows its formula. You can redo any of them for your own pool - see our methodology for the constants and the full working.

Everything in this section

Every page in this section

A water testing vial and reagent kit being used to check pool chemistry

Best test kit

Best Pool Test Kits

Titration kits, color comparators, strips and a photometer compared on precision, speed and what each one cannot see.

Top pick

AquaChek Select Connect 7-Way Test Strips, complete kit

Weekly testing you will actually do

Check price on Amazon

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Questions people actually ask

What order should I balance pool water in?
Total alkalinity, then pH, then cyanuric acid, then chlorine. Alkalinity is the buffer that keeps pH stable, so correcting pH first on a pool with low alkalinity means doing it again within days.
What are the correct pool chemistry levels?
Free chlorine 1 to 4 ppm for routine sanitizing, pH 7.2 to 7.6, total alkalinity 80 to 120 ppm, and cyanuric acid 30 to 50 ppm on a tablet pool or 60 to 80 ppm on a saltwater one. Those figures come from HTH's own product pages, which are the manufacturer sources the regulatory framework points at.
How often should I test my pool water?
Free chlorine and pH weekly during the season, and after anything unusual - a storm, a party, a heavy dose of anything. Cyanuric acid, calcium hardness and phosphate a few times a season, since none of them changes quickly.
Why does my chlorine reading look fine when the pool is green?
Almost always cyanuric acid. Above roughly 50 ppm, stabilizer progressively blunts chlorine's effectiveness, so the number on your test is no longer telling you what the chlorine is actually doing. See cyanuric acid.

Sources

Every figure on this page traces to one of these. Where a number could not be sourced, the page says so rather than estimating.

Why there is nothing to buy here: This is the section's front door. The kits and chemicals sit on the roundups below, each with its top pick priced and linked, because a hub of bare text links is a hub with nothing to buy.