Cloudy pool water: 7 common causes and how to fix them

Cloudy water is frustrating because it feels vague: you add chlorine, run the pump, vacuum… and the pool still looks hazy. In Costa Rica this happens often due to heavy rain, high humidity and vegetation, and year-round pool use.

The good news: cloudy water almost always has a clear cause. The bad news: if you treat it with random products, you’ll spend more and the problem returns.

Here are 7 common causes—and a practical order of operations.

Start by identifying the type of cloudiness

Gray/white haze
Often fine particles, weak filtration, or pH/alk issues.

Greenish haze
Often early algae or ineffective chlorine due to high demand.

Brown/yellow tint
Common after storms: sediment/organic load, sometimes minerals/metals.

Cause 1: Not enough filtration (run time or undersized system)

Rain and organic debris increase system load in Costa Rica. If circulation is too short, the pool never fully clears.

Fix

• Extend filtration temporarily (recovery mode 24–48h if needed).
• Check flow and return strength.
• Confirm the filter and pump are sized for real volume and use.

Cause 2: Dirty filter or worn filter media

A saturated filter won’t capture fine particles effectively.

Fix

• Clean the filter properly (based on filter type).
• Check media condition (old sand, overloaded cartridges).
• Ensure proper backwash and rinse procedures.

Cause 3: pH / alkalinity out of range

Many treatments fail because pH is high or unstable. High pH can reduce chlorine effectiveness and create “milky” water.

Fix

• Stabilize pH first.
• Then correct alkalinity if pH keeps drifting.
• Then address chlorine/shock if needed.

Cause 4: Low chlorine or high organic demand (especially after rain)

After rain, chlorine demand spikes. Water can turn cloudy even if you “added chlorine” earlier.

Fix

• Maintain a stable chlorine residual.
• Combine with brushing, skimmer cleaning, and extended filtration.
• If algae signs appear, treat it as algae (not just clarifier).

Cause 5: Fine particles your filter isn’t catching

Storm dust and fine sediment can require optimal filtration and (sometimes) controlled clarification.

Fix

• Optimize filtration first.
• If using clarifier, dose correctly and run proper filtration.
• If using flocculant, treat it as a controlled process (settle, then vacuum to waste).

Cause 6: Poor circulation (dead spots)

Good pumps still fail if water movement is weak in corners.

Fix

• Aim returns for proper circulation.
• Brush walls and floor (biofilm won’t “chemically disappear”).
• Check skimmers, returns, and suction points.

Cause 7: Minerals/metals or chemical precipitation

Less common, but can cause sudden haze or discoloration—especially with high pH and certain products.

Fix

• Avoid “mixing cocktails” of chemicals.
• Control pH before corrective treatments.
• If metals are suspected, address with a targeted approach (not random chlorine dumping).

A simple, no-guess diagnostic method

1. Verify filtration + physical cleaning
2. Stabilize pH first
3. Decide: organic (green) vs particles (gray)
4. Change one variable at a time and reassess in 24 hours

Final recommendation

In Costa Rica, cloudy water is usually a combination of filtration, water balance, and rain-driven organic load. The fastest way back to crystal water is to correct the cause in the right order—rather than adding more products.

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