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How to Lower Chlorine in a Pool
Sun and time bring chlorine down. To get there faster, swap part of the water.
1 of 3: your gallons
The share of water to swap appears here.
- Sun
- burns off a few ppm a day
- Dilute
- drain a share, refill with tap water
- Neutralizer
- sodium thiosulfate, sold for spas
The easiest way to lower chlorine in a pool is to simply wait. Sunlight eats a few ppm of free chlorine every day. A ppm is a part per million, which is the figure your test strips or kit give you. When you want a faster result, swap out some of the water or add a chlorine neutralizer.
- Where you want free chlorine to sit: 3 to 5 ppm with 30 ppm of stabilizer, 4 to 6 ppm with 40 ppm
- Sunlight: takes off a few ppm daily
- Quickest fixes: a partial water change, or a neutralizer
Letting sunlight and time handle it
Pull the cover off and let the sun reach the water. It is free, and it usually does the job.
Keep the pump going too, along with any fountains or water features. Moving water mixes air in, and that helps the level drop evenly instead of in patches.
After a day, test again so you know where you stand.
Replacing part of the water
When time is short, drain off some water and top up from the tap. Tap water thins the chlorine out, so the level drops in step with how much you swap.
Stabilizer is cyanuric acid, or CYA, the chemical that protects chlorine from sunlight. It never breaks down and no filter removes it, so water replacement is the only way to reduce it. Draining lowers stabilizer along with chlorine, so keep that in mind before you start.
To find how much water to replace, take 1 minus the target over the current level. Say you want to go from 100 ppm to 50 ppm, that means changing out about half the pool. If you know your pool's volume in gallons, you can judge the amount you need to swap.
Using a chlorine neutralizer
A neutralizer is a product that wipes out chlorine. Look for sodium thiosulfate, the kind sold for use in spas. It goes to work within minutes.
The common mistake is adding too much and dropping chlorine past the level you wanted. Start small, test, and only add more if the number says so.
When is chlorine too high to swim?
Once you go past the shock level that matches your stabilizer, the water may sting eyes and dull swimsuit colors. Stay below that line and most people can swim without a problem.
Give a pool time after shocking. Swim once free chlorine is back in the normal range for your stabilizer and no higher than 10 ppm. With an ordinary dose of liquid chlorine, about 30 minutes is enough before you get back in.
Handling chemicals safely
Before anything goes into the pool, start the pump. Add chemicals one at a time, right where a return jet pushes water out, so each one spreads fast.
Acid and chlorine should never meet, since they react badly. When you use acid, always pour it into water, never the other way around.