How the doses are worked out

The charts we use

Of the 85 figures, 45 come from official sources: US state, county and city health departments, CDC's model code for public pools and its guidance pages, and NIST for unit conversions. 34 come from makers, retailers, trade and industry articles, a water utility page and one sports federation, each labeled "Other source" in the lists at the bottom of the pages that use them. 6 figures we couldn't confirm. The calculators give no number for them; where one would matter, they tell you to follow your label.

Dose charts are written per 10,000 US gallons, and the calculators scale them to your pool.

Why we start low

Where sources disagree, the calculators use the smaller amount, then ask you to retest. Too much of a chemical takes another chemical, or a partial drain, to undo; too little only needs another round. Where a chart gives a dose for a big change, the calculators give a first part and ask you to retest before the rest. Amounts are rounded down.

When we say ask a professional

The calculators give no amount, and say ask a pool professional, when:

• the water is green, black or very cloudy;
• a reading is at or beyond the end of a standard test's scale, or far outside the normal range;
• the pool is a hot tub, or a public or commercial pool (every chemical calculator asks how the water looks and what type of pool it is);
• the pool is smaller than 500 or larger than 60,000 US gallons.

How the figures were checked

Every figure was checked against its source page; open a figure under "The charts behind this page" to see when. A second checker re-opened the sources on 11/9/2026 and checked 82 figures; 68 of the figures shown today match what that checker saw. On 11/10/2026, 34 key figures were looked up again by a checker who couldn't see ours: 23 came back the same, 10 were partly different, and 1 came back with a weaker source. No calculator amount changed as a result.

Tests behind the calculators

The sums are tested every time the site is built: 315 tests, including 44 amounts printed in published charts, labels and manuals, 88 tests of the limits where a calculator gives a smaller round or no amount, and 39 tests that the safety lines and warnings appear. If any test fails, the site isn't built. Every result carries the same 13 safety lines.