How Much Chlorine

Cyanuric Acid Calculator: How Much Stabilizer to Add to a Pool

By Tam Vu · Updated

On this page
  1. Ranges to know
  2. The formula
  3. Cyanuric acid for +10 ppm
  4. If the reading is too high
  5. Products that already add it
  6. Safety and the label
  7. Sources

Cyanuric acid, often called CYA or stabilizer, is a pool chemical you add by weight. Test your water, pick a target, and the amount follows from your pool's volume.

Cyanuric acid

The 20 and 40 ppm values are example numbers only. Use your own test reading. If your target is below your reading, the calculator shows how much water to replace, because chemicals cannot remove cyanuric acid.

Ranges to know

Columbus Public Health's water chemistry sheet, a standard for public pools, lists cyanuric acid below 70 ppm, ideally 30 to 50 ppm, and says a pool above 100 ppm should be closed (Columbus Public Health). Treat these as reference points for a home pool.

Two CDC points matter if you use it (CDC):

  • A pool that uses cyanuric acid should keep free chlorine at 2 ppm or more, instead of the 1 ppm minimum for pools without it.
  • The CDC advises against using cyanuric acid in hot tubs.

See the chemistry levels chart for all the ranges together.

The formula

Cyanuric acid is dosed by its own weight. With 1 ppm equal to 1 mg per liter:

grams of cyanuric acid = gallons × 3.785 × ppm to add ÷ 1,000 ÷ (strength on label ÷ 100)

For a product labeled 100% cyanuric acid, that is about 13.4 oz per 10 ppm in 10,000 gallons. The Indiana Department of Health's chemical adjustment sheet lists 13 oz for the same case (Indiana DOH).

Example: a 15,000-gallon pool reads 20 ppm and you want 40. Add 20 ppm: 15,000 × 3.785 × 20 ÷ 1,000 = 1,136 g, which is 2.5 lb of 100% cyanuric acid.

Cyanuric acid for +10 ppm

Pool size 100% cyanuric acid for +10 ppm
5,000 gallons 6.7 oz
10,000 gallons 13.4 oz
15,000 gallons 1.25 lb (20.0 oz)
20,000 gallons 1.67 lb (26.7 oz)
30,000 gallons 2.50 lb (40.1 oz)

For a bigger rise, scale in proportion: +30 ppm takes three times these amounts. If your product label shows a strength below 100%, divide by that fraction.

If the reading is too high

Chemicals cannot remove cyanuric acid. The only way down is replacing pool water with fresh water. If the fill water has none, the share to replace is 1 − target ÷ current. For example, from 120 ppm down to 50 ppm: 1 − 50 ÷ 120 = 58%, about 8,750 gallons in a 15,000-gallon pool. The calculator above does this when you enter a lower target.

Products that already add it

Trichlor and dichlor chlorine products contain cyanuric acid, so using them raises the reading over time. Test before adding more. See how much chlorine to add for those products.

Safety and the label

The calculator works from the strength you select; the label on your product is the final word. Virginia's Department of Health says to mix chemicals only as the label directs, add chemicals to water and never water to chemicals, store liquids below dry products in their original containers, and wear the protective gear the label lists (VDH).

Sources