Why Is My Pool Cloudy? 6 Causes and How to Fix Each One

Cloudy pool water is one of the most common complaints from pool owners, and it can mean several different things. The fix depends on the cause. Here are the six most likely reasons and how to address each one.

1. Low Free Chlorine

This is the most common cause. When free chlorine drops below 1 ppm, bacteria and algae start growing faster than the chlorine can kill them. The early stage looks like slightly hazy or dull water before turning green. Test your free chlorine and if it's below 1 ppm, shock the pool. Use enough liquid chlorine to bring FC to 10 ppm or higher for a proper shock. Run the pump continuously until the water clears, which can take 24-48 hours.

2. High pH

When pH rises above 7.8, calcium and other minerals start coming out of solution and creating tiny suspended particles. This gives the water a milky, cloudy appearance. Even worse, high pH makes your chlorine less effective, so you're fighting two problems at once. Lower your pH with muriatic acid and the cloudiness often clears on its own as the minerals go back into solution.

3. High Total Alkalinity

Very high alkalinity (above 150 ppm) can cause calcium to precipitate out of the water, similar to high pH. It also makes pH resistant to change, creating a cycle where pH stays high and cloudiness persists. Lower TA with muriatic acid using the acid-and-aerate method.

4. Poor Filtration

If your filter isn't running long enough or isn't working properly, particles stay suspended in the water. Your filter should run at least 8-10 hours per day, and the filter media needs to be clean. For sand filters, check the pressure gauge. If it's 8-10 psi above the clean baseline, it's time to backwash. For cartridge filters, inspect and clean or replace the cartridge. A filter that's past its useful life won't clear the water no matter how long it runs.

5. High Calcium Hardness

Calcium above 400 ppm can cause a persistent haze, especially in warm water. Calcium scale forms on surfaces and in the water itself, creating a cloudy or dull appearance. The fix is to partially drain and refill with fresh water to lower the calcium level. There's no chemical that removes calcium from pool water.

6. Algae (Early Stage)

Before algae turns your pool green, it starts as a subtle cloudiness or a slightly dull look to the water. If the walls or floor feel slippery, that's algae biofilm even if the water still looks blue. The fix is the same as low chlorine: shock the pool hard. Brush all surfaces first to break up the biofilm so the chlorine can reach the algae. Run the pump continuously until the water is clear, then vacuum or backwash the dead algae.

The Fastest Path to Clear Water

Start by testing everything: chlorine, pH, alkalinity, calcium. Most cloudiness is caused by chemistry, and fixing the chemistry fixes the water. If all your levels are perfect and the water is still cloudy, the problem is filtration. Pool Clarity can help you diagnose which chemical is off and tell you exactly how to fix it.