Pool Water Chemistry

Test before you treat

Test your water before adding anything, then dose by your pool's volume using the directions on the label. Retest after the water has circulated.

Pool chemicals at a glance

• Sodium bicarbonate / alkalinity increaser: raises total alkalinity.
• Soda ash / pH increaser: raises pH.
• Sodium bisulfate / pH minus, muriatic acid: lower pH and alkalinity.
• Calcium chloride / calcium increaser: raises calcium hardness.
• Cyanuric acid / stabilizer: helps protect chlorine from sunlight in outdoor pools.
• Chlorine, bromine and shock: sanitize the water and oxidize contaminants.
• Clarifiers and stain control: help with cloudy water, metals and scale.

Handle chemicals safely

Never mix chemicals together, and never mix different types of chlorine. Add chemicals to water, not water to chemicals, one product at a time. Wear gloves and eye protection, store products sealed in a cool, dry, ventilated place away from each other, and keep them out of reach of children and pets.

Pool Water Chemistry FAQs

How do I choose the right pool chemical?

Choose a pool chemical by testing your water first and treating only the reading that is out of range. Raise total alkalinity with sodium bicarbonate, raise pH with soda ash, lower pH with sodium bisulfate (pH minus) or muriatic acid, raise calcium hardness with calcium chloride, and keep chlorine or bromine in range to sanitize. Dose by your pool's volume, following the label.

What is pool stabilizer used for?

Pool stabilizer, or cyanuric acid, protects the free chlorine in an outdoor pool from being used up by the sun's UV rays; Taylor describes it as sunblock for chlorine. Taylor's ideal range is 30 to 50 ppm, and the maximum, typically 100 ppm, is set by local codes. It is mainly used in outdoor pools, so test cyanuric acid before adding any.

What does pool shock do, and when should I shock my pool?

Pool shock breaks up combined chlorine (chlorine bound to contaminants) by raising free chlorine to about 5 to 10 ppm. Hayward suggests shocking every couple of weeks in the swim season, after heavy use or storms, and when opening and closing the pool. Shock in the evening so sunlight does not burn off the chlorine, and swim again once free chlorine is back to 1 to 3 ppm.

In what order should I balance my pool water chemistry?

Balance pool water by adjusting total alkalinity first, then pH, because Hayward explains that alkalinity in the 80 to 120 ppm range acts like a ceiling on pH and keeps it from swinging quickly. Once both are in range, check calcium hardness and your chlorine or bromine level. Add one product at a time and retest with a pool water test kit after the water circulates.

What happens if my pool's pH is too high or too low?

If pool pH is too high, chlorine loses effectiveness and scale can build up, and if it is too low, the water becomes corrosive. Taylor's ideal pH is 7.4 to 7.6, and Hayward treats 7.2 to 7.8 as balanced. Raise pH with soda ash and lower it with sodium bisulfate (pH minus) or muriatic acid, following the dosing on the label.

Why does calcium hardness matter in a pool?

Calcium hardness matters because pool water that is too low in calcium becomes aggressive and can leach minerals from pool walls and grout, while very high calcium can make the water cloudy. Taylor's ideal range for pools is 200 to 400 ppm, and Hayward suggests 175 to 300 ppm for vinyl pools. Calcium chloride raises calcium hardness.

Why does my pool smell strongly of chlorine?

A strong chlorine smell in a pool usually comes from combined chlorine, not from too much chlorine. Taylor explains that combined chlorine forms when chlorine reacts with organic material, and recommends keeping it below 0.4 ppm. Hayward says shocking, which raises free chlorine to 5 to 10 ppm, breaks combined chlorine up. Test both free and total chlorine to see how much is combined.