Pool Chemical Dose by Product Strength

This page keys off the strength printed on your product, which is the number that actually changes the answer: 2.4 oz of 56% dichlor and 1.9 oz of 73% calcium hypochlorite do the same job. If you do not know your pool’s volume yet, or you also need pH and total alkalinity, the pool chemistry page works volume out from your dimensions and doses all three together. Both pages run the same arithmetic.

Pool chemicals are dosed based on pool volume and target concentration in ppm.

Chlorine dosing formula:

• Grams needed = (Volume in liters × Target ppm) / (% active chlorine × 10)
• Ounces needed = Grams / 28.3495

Common chlorine products:

Ideal chlorine levels:

• Free chlorine: 1-3 ppm (residential pools)
• Shock treatment: 10-30 ppm (superchlorination)

Pool volume estimation:

• Rectangular: Length × Width × Avg Depth × 7.48 (gallons) or × 1000 (liters if in meters)
• Round: Diameter² × Avg Depth × 5.9 (gallons)

Volume conversions:

• 1 US gallon = 3.785 liters
• 1,000 gallons = 3,785 liters

To raise chlorine by 1 ppm in 10,000 gallons:

• Liquid bleach (12.5%): ~10.2 fl oz (303 mL)
• Cal-hypo (65%): ~2 oz (58 g)
• Trichlor (90%): ~1.5 oz (42 g)

That first line is the one to memorise, because it doubles as a sanity check: a full US gallon of 12.5% liquid chlorine raises 10,000 gallons of water by about 12.5 ppm. Note that liquid chlorine is sold on a different basis from the granulars. Its percentage is grams of available chlorine per 100 mL of liquid, while cal-hypo, dichlor and trichlor are rated by weight. Treating the liquid figure as a weight percentage under-doses by roughly a sixth.

The strength differences in that list matter more than they look, because they change how much you pour. Liquid chlorine is only 10 to 12.5% available chlorine, while cal-hypo granular is 65 to 73%, so you need roughly five times less of the granular for the same effect. Dose by the percentage, not by habit, or you’ll wildly over- or under-treat the water.

Two things trip up new pool owners. First, cyanuric acid (stabilizer) protects chlorine from sunlight, but too much of it locks the chlorine up so it stops sanitizing, the dreaded “chlorine lock” where your test shows chlorine present yet the water still goes green. The only real fix is diluting with fresh water. Second, never mix pool chemicals together, and never pour water into acid; always add acid to water, slowly, and ideally treat in the evening so the sun doesn’t burn off the chlorine before it works. Test first, dose once, retest the next day, and resist the urge to dump everything in at once.