Cloudy pool water means tiny particles are floating in your pool that the filter isn't catching. It's rarely just one thing. Here's what causes a cloudy pool, the steps we follow to clear it, and how long it usually takes.
Why Is My Pool Cloudy?
These are the causes we run into most on pools across Santa Clarita and the San Fernando Valley. Often it's two or three of them at once.
- Low chlorine. When chlorine drops, bacteria and early algae cloud the water before you ever see green.
- Phosphates. Leaves, pollen, dirt, and fertilizer bring phosphates into the pool, and phosphates feed algae. When the chlorine looks fine and the water is still hazy, phosphates are often the hidden cause.
- High calcium. Valley water is hard. When calcium runs high, especially with a high pH, it comes out of the water and turns it milky.
- A dirty filter. A clogged filter can't catch fine particles, so they keep circulating.
- Short filter run time. If the pump and filter don't run long enough each day, the water never gets fully filtered.
- Leaves and debris. Anything left sitting in the pool breaks down and feeds every problem above.
- Dead algae. After shocking an algae bloom, the dead algae leaves the water cloudy until it's removed.
The time of year matters. In the fall, heavy leaf drop loads the pool with debris and phosphates, and we see a lot more cloudy pools as a result.
How We Clear Cloudy Pool Water
Every cloudy pool gets the same process. Testing comes first, because the right fix depends on the real cause.
Test the water
Always step one. We check chlorine, pH, alkalinity, calcium, and phosphates. Guessing wastes chemicals and time, and cloudy water often has more than one cause.
Clean out the debris
We skim the surface, empty the skimmer and pump baskets, brush the walls and floor, and vacuum. Leaves sitting in the pool keep feeding the problem.
Balance the chemistry
We bring pH and alkalinity into range and raise the chlorine. If calcium is high, we adjust the plan around it so it stops coming out of the water.
Backwash and add fresh DE
A good backwash followed by new DE is part of almost every cloudy pool we fix. On a cartridge filter, we clean the cartridges or replace them if they're worn out.
Treat phosphates if they're high
If the test shows high phosphates, we add a phosphate remover. Otherwise algae keeps coming back no matter how much chlorine goes in.
Add clarifier or floc
For a light to medium haze, a clarifier helps the filter catch the fine particles. For heavy cloudiness or dead algae, we use floc and vacuum the pool to waste.
Run the filter longer
This is the step people skip. The filter has to run much longer than its normal schedule until the water clears. A short run time is how a lot of pools get cloudy in the first place.
Retest and follow up
We retest over the next several days and adjust. Most pools are clear within the week.
Why a DE Filter Is So Good at Clearing Cloudy Water
DE stands for diatomaceous earth, a fine powder that coats the grids inside the filter. That coating traps much smaller particles than a sand or cartridge filter can. Those tiny particles are exactly what makes water look cloudy.
The catch is that DE only works when it's fresh. As the coating fills up with dirt, the filter catches less and less. That's why a backwash followed by new DE is part of almost every cloudy pool we fix. If you have a cartridge filter, cleaning the cartridges does the same job, and worn cartridges should be replaced.
Whatever filter you have, a clean filter and a longer run time do more to clear cloudy water than any bottle of chemicals.
When to Add a Pool Clarifier
It depends on how cloudy the pool is.
Clarifier is for mild to moderate haze. It clumps tiny particles together so the filter can catch them. You add it with the filter running, and it works alongside a clean filter, not in place of one.
Floc, short for flocculant, is for heavy cloudiness, like dead algae after a shock. It drops everything to the bottom of the pool. Then the pool has to be vacuumed to waste, so the debris goes out of the pool instead of back into the filter.
Don't use clarifier and floc together, and don't add clarifier until the chemistry is balanced. If the chlorine is low or the phosphates are high, the cloudiness will just come back.
How Long Does It Take to Clear a Cloudy Pool?
A light haze can clear in a day or two once the chemistry is balanced and the filter is clean. A very cloudy pool takes longer, especially if dead algae is involved.
We tell customers to plan on a week. That gives the filter time to work and the chemistry time to settle, and it leaves room for a second round of treatment if it's needed.
One of our clients has a big tree hanging right over the pool, and the water gets foggy often. What clears it every time is the same routine: backwash the filter, add fresh DE, bring the chlorine up, and run the filter longer.
How to Keep Your Pool From Getting Cloudy Again
- Keep up with debris, especially in the fall. Skim often and empty the baskets.
- Keep chlorine steady. Test regularly instead of waiting for the water to change.
- Check phosphates, particularly if trees or plants hang over the pool.
- Run the filter long enough every day, and longer when the pool sees heavy use or a lot of debris.
- Backwash and recharge the DE on a regular schedule, or clean your cartridges.
New to pool care? Our pool maintenance guide for beginners covers the weekly routine. If the filter itself seems to be the problem, our pool repair team can take a look.
Still Fighting Cloudy Water?
If your pool won't clear, give GK Swimming Pools a call. We're a family-run company, three generations in, and our weekly pool service keeps water clear across Santa Clarita and the San Fernando Valley. We'll find the real cause and get your pool back to swimmable.