Pool Chemical Levels, Explained

Start with the numbers. Everything else on this page explains them.

Your pool’s equipment manuals, especially for a salt system or a heater, may give slightly different ranges. Follow those where they differ.

Fix things in this order

The most common way to waste money on chemicals is to chase pH and chlorine before alkalinity is right. Alkalinity pulls pH around, so if it is off, any pH adjustment drifts back within days.

1. Test everything first. A good liquid kit or a store water test beats a single strip for this.
2. Adjust total alkalinity. Sodium bicarbonate raises it. Acid lowers it, slowly.
3. Adjust pH. Once alkalinity is in range, pH usually needs only a small correction.
4. Bring chlorine into range, or shock if the water is cloudy, green, or has had heavy use.
5. Calcium and stabilizer last. They change slowly and rarely need weekly attention.

Run the pump while adding chemicals, add them one at a time, and give each one a few hours of circulation before you add the next or retest.

What each product is for

Chlorine comes as slow-dissolving tablets (usually trichlor, which also adds stabilizer), granular shock, or liquid. Salt pools make their own from dissolved salt, but it is still chlorine doing the work.

Shock is a large dose that burns off contaminants and combined chlorine, the compound behind that “pool smell” people wrongly blame on too much chlorine. Shock in the evening, so the sun doesn’t destroy it before it does its job.

Algaecide is a backup, not a substitute for chlorine. It is most useful at closing and during long hot spells.

Balancers are the pH increaser and decreaser, alkalinity increaser and calcium increaser products that move individual readings.

Clarifiers and enzymes help the filter catch fine particles and break down oils from sunscreen. They help, but they won’t fix poor filtration.

The stabilizer trap

Here is a trade-off we see every summer. Chlorine tablets are convenient, and most contain stabilizer. Every tablet adds a little more. Stabilizer doesn’t evaporate or get used up, so over a long season it climbs, and as it climbs the same chlorine reading becomes less effective. Pools that look fine in June can turn cloudy in August with a “normal” chlorine number.

The only real fix for very high stabilizer is to drain and replace some of the water. If you use tablets all season, have stabilizer tested a couple of times along the way rather than only at opening.

Storing chemicals safely

• Keep products in their original, closed containers, in a cool, dry, ventilated spot out of children’s reach.
• Never mix chemicals together, and never store chlorine products near acid. The gas they produce together is dangerous.
• Always add chemicals to water, never water to chemicals.
• Use a clean, dry scoop for each product.
• Wear gloves and eye protection when handling acid or shock.

Questions we get asked

How often should I test pool water?

Chlorine and pH two or three times a week in summer, and after storms, parties or heat waves. Alkalinity weekly. Calcium and stabilizer every few weeks.

Why do my eyes sting if the chlorine is fine?

Usually pH is off, or combined chlorine has built up. Test pH first, then consider shocking.

Can you test my water in store?

Bring a sample to our retail store on Leslie Street and ask. Take it from elbow depth, away from the return jets, in a clean bottle.

If balancing the water every week is more than you want to take on, our weekly pool service includes testing and pool chemical balancing in Toronto and York Region.