First, test the water
Do not add anything until you have numbers. Cloudy water is a symptom, and guessing usually makes it worse. Test free chlorine, pH, total alkalinity, and cyanuric acid. If your free chlorine is low for your CYA level, that alone explains most cloudiness, because the chlorine cannot keep up and the water is starting to grow what you cannot see yet.
If you only have strips, get a real reading before dosing. The amount of chlorine to add depends on your volume and current level, which the chlorine calculator works out exactly.
Fix chlorine and pH first
Bring free chlorine up to the right level for your stabilizer. If the pool is heading toward green or has not held chlorine, treat it as an early algae problem and raise FC to the shock level for your CYA, which the shock calculator sets for you. Keep it there until the water clears.
Then check pH. High pH is a very common cause of cloudiness on its own, because it lets calcium fall out of solution and dulls the water. Bring pH back to the 7.4 to 7.6 range with the pH calculator. Cloudy water that is chemically fine is usually a filtration problem instead.
Run and clean the filter
Cloudiness is suspended particles, and the filter is what removes them. Run the pump continuously, 24 hours a day, until the water clears. A few hours a day is not enough when you are fighting cloudiness.
A dirty filter cannot clear a pool. Backwash a sand or DE filter, or rinse a cartridge, then keep running it. If the filter pressure is high, that is a sign it needs cleaning. This step alone clears a lot of pools once the chemistry is right.
Speed it up with a clarifier or flocculant
If the chemistry is right and the filter is running but the water is still hazy, a clarifier helps. It clumps the fine particles together so the filter can catch them. It is gentle and works over a day or two.
For a fast, heavy-duty fix, a flocculant drops everything to the floor as a cloud you then vacuum to waste (not through the filter). It clears water quickly but wastes water and takes effort. Use clarifier for normal haze and flocculant only when you need the pool clear in a hurry.
Check your water balance
If a pool keeps going cloudy, the underlying balance is usually off. Very high calcium hardness, high pH, and high alkalinity together push the water toward scaling and persistent cloudiness. Run your numbers through the saturation index calculator to see whether the water is balanced, and adjust whatever is pulling it out of range.
Frequently asked questions
Why is my pool cloudy?
The usual causes are low free chlorine for your CYA level, high pH, a dirty or under-run filter, or fine debris the filter has not caught yet. Test the water first, fix chlorine and pH, then run and clean the filter. Most cloudy pools come down to one of those.
How long does it take to clear a cloudy pool?
With the chemistry corrected and the filter running 24 hours a day, a mildly cloudy pool often clears in a day or two. A clarifier can speed it up; a flocculant clears it fastest but means vacuuming to waste. A pool turning green takes longer because you have to hold shock level until it passes.
Will shock clear a cloudy pool?
It helps if the cause is low chlorine or early algae, which is common. Raise free chlorine to the shock level for your CYA and hold it there while the filter runs. But if the cause is high pH or a dirty filter, shock alone will not fix it, so test first.
Should I use a clarifier or a flocculant?
Use a clarifier for normal haze; it clumps particles so the filter removes them over a day or two, with little effort. Use a flocculant only when you need the pool clear fast, since it drops everything to the floor and you must vacuum it to waste, wasting water.
Can a dirty filter make a pool cloudy?
Yes, very often. The filter is what removes the suspended particles that make water cloudy, so a clogged filter or one that only runs a few hours a day cannot keep up. Clean or backwash the filter and run the pump continuously until the water clears.