Chlorine & Shock
How much of which product to raise free chlorine by a given amount.
Every chemical dose a pool will ever need is volume × a constant. Which means the single most valuable number in pool care is the volume — and most people are using the figure from a brochure rather than one they measured.
Get the gallons wrong by a fifth and every dose for the life of the pool is wrong by a fifth, in the same direction, forever.
Volume
Rectangular pools are length × width × average depth × 7.48. Round pools use π r². Oval pools use π ÷ 4 × length × width. Average depth on a sloped floor is (shallow + deep) ÷ 2 — exact for a straight slope, an approximation for anything with a bench or a step-down.
7.48 gallons per cubic foot is a conversion constant, not an estimate.
Chlorine products are not interchangeable
To raise free chlorine 1 ppm in 10,000 gallons takes about 2 oz of cal-hypo, 2.3 oz of dichlor, 1.5 oz of trichlor, 10.7 fl oz of liquid chlorine, or 16 fl oz of household bleach.
That is the easy half. The hard half is what each one also adds:
- Cal-hypo adds calcium hardness. In hard water it is what scales the tile line and the heater.
- Dichlor and trichlor add cyanuric acid, and trichlor is strongly acidic besides.
- Liquid chlorine adds only salt, and nudges pH up.
Cyanuric acid is the trap
CYA protects chlorine from sunlight, which is why stabilised products exist and why an outdoor pool needs some. But above roughly 50 ppm it binds chlorine so tightly that the chlorine stops killing anything — and CYA does not break down. It leaves only by dilution.
A season of trichlor tablets is the standard route to a pool that reads plenty of chlorine and still goes green. Draining and refilling is the cure, and it is the expensive one.
How to dose
Pump running. Slowly, at the deep end or through the skimmer. Granules resting on a vinyl liner bleach it permanently.
Test after four hours of circulation, not immediately — a reading taken beside the return jet is a reading of the return jet.
Chlorine dose by pool volume
4,500 calculations · browse all
- How much liquid chlorine for a 12 ft round pool to raise chlorine 1 ppm
- How much cal-hypo for a 12 ft round pool to raise chlorine 5 ppm
- How much trichlor for a 15 ft round pool to raise chlorine 2 ppm
- How much cal-hypo for a 15 ft round pool to raise chlorine 2 ppm
- How much trichlor for a 18 ft round pool to raise chlorine 1 ppm
- How much liquid chlorine for a 18 ft round pool to raise chlorine 1 ppm
- How much dichlor for a 21 ft round pool to raise chlorine 5 ppm
- How much liquid chlorine for a 21 ft round pool to raise chlorine 5 ppm
- How much dichlor for a 24 ft round pool to raise chlorine 2 ppm
- How much trichlor for a 24 ft round pool to raise chlorine 1 ppm
- How much cal-hypo for a 27 ft round pool to raise chlorine 1 ppm
- How much trichlor for a 27 ft round pool to raise chlorine 5 ppm
- How much cal-hypo for a 30 ft round pool to raise chlorine 5 ppm
- How much dichlor for a 30 ft round pool to raise chlorine 2 ppm
- How much liquid chlorine for a 33 ft round pool to raise chlorine 2 ppm
- How much dichlor for a 33 ft round pool to raise chlorine 1 ppm
- How much liquid chlorine for a 12 × 24 ft oval pool to raise chlorine 1 ppm
- How much cal-hypo for a 12 × 24 ft oval pool to raise chlorine 5 ppm
- How much trichlor for a 15 × 30 ft oval pool to raise chlorine 2 ppm
- How much cal-hypo for a 15 × 30 ft oval pool to raise chlorine 2 ppm
- How much trichlor for a 16 × 32 ft oval pool to raise chlorine 1 ppm
- How much liquid chlorine for a 16 × 32 ft oval pool to raise chlorine 1 ppm
- How much dichlor for a 18 × 33 ft oval pool to raise chlorine 5 ppm
- How much liquid chlorine for a 18 × 33 ft oval pool to raise chlorine 5 ppm
- How much dichlor for a 18 × 36 ft oval pool to raise chlorine 2 ppm
- How much trichlor for a 20 × 40 ft oval pool to raise chlorine 1 ppm
- How much cal-hypo for a 20 × 40 ft oval pool to raise chlorine 1 ppm
- How much trichlor for a 10 × 20 ft rectangular pool to raise chlorine 5 ppm
- How much cal-hypo for a 10 × 20 ft rectangular pool to raise chlorine 5 ppm
- How much dichlor for a 12 × 24 ft rectangular pool to raise chlorine 2 ppm
- How much liquid chlorine for a 12 × 24 ft rectangular pool to raise chlorine 2 ppm
- How much dichlor for a 14 × 28 ft rectangular pool to raise chlorine 1 ppm
- How much liquid chlorine for a 14 × 28 ft rectangular pool to raise chlorine 1 ppm
- How much cal-hypo for a 15 × 30 ft rectangular pool to raise chlorine 5 ppm
- How much trichlor for a 15 × 30 ft rectangular pool to raise chlorine 2 ppm
- How much cal-hypo for a 16 × 32 ft rectangular pool to raise chlorine 2 ppm
- How much trichlor for a 16 × 32 ft rectangular pool to raise chlorine 1 ppm
- How much liquid chlorine for a 16 × 36 ft rectangular pool to raise chlorine 1 ppm
- How much dichlor for a 16 × 36 ft rectangular pool to raise chlorine 5 ppm
- How much liquid chlorine for a 18 × 36 ft rectangular pool to raise chlorine 5 ppm
- How much dichlor for a 18 × 36 ft rectangular pool to raise chlorine 2 ppm
- How much trichlor for a 20 × 40 ft rectangular pool to raise chlorine 1 ppm
- How much cal-hypo for a 20 × 40 ft rectangular pool to raise chlorine 1 ppm
- How much trichlor for a 20 × 44 ft rectangular pool to raise chlorine 5 ppm
- How much cal-hypo for a 20 × 44 ft rectangular pool to raise chlorine 5 ppm
- How much dichlor for a 25 × 45 ft rectangular pool to raise chlorine 2 ppm
- How much liquid chlorine for a 25 × 45 ft rectangular pool to raise chlorine 2 ppm
- How much dichlor for a 30 × 50 ft rectangular pool to raise chlorine 1 ppm