Green Pool Water in Costa Rica: Real Causes and How to Fix It

Owning a pool in Costa Rica has a big advantage: you can enjoy it year-round. But tropical conditions also bring challenges—heavy rain, humidity, strong sun, and organic debris (leaves, dust, soil). In this environment, a pool can turn green quickly if water chemistry and filtration fall out of balance.

Why does pool water turn green?

Most of the time, green water is caused by algae growth. Algae develops when the pool doesn’t have enough effective free chlorine, filtration is not keeping up, or water balance prevents disinfectants from working properly.

In Costa Rica, the risk increases due to:

• Rainy season: adds water, dirt, and nutrients while diluting chemicals
• Strong UV exposure: breaks down chlorine faster
• Frequent use: increases demand on sanitation and filtration

Real causes of green pool water

1) Chlorine is present, but not effective

If pH is too high, chlorine becomes much less effective—even if you “have chlorine” in the water.

Typical sign: water turns green and visibility drops.

2) Filtration time is too short (or equipment is undersized)

If the pump and filter don’t circulate enough water, algae and fine particles accumulate.

Typical sign: constant haze or dust settling on the floor.

3) No brushing (algae sticks to surfaces)

Algae clings to walls, corners, steps, and ledges. Without brushing, treatments take longer and problems repeat.

4) Rain and organic load

Leaves, soil, pollen, and runoff feed algae—especially during rainy weeks.

5) Stabilizer (cyanuric acid) out of range

If stabilizer is too high, chlorine can become sluggish. This often happens with continuous use of chlorine tablets.

How to fix green water in Costa Rica (practical plan)

Step 1: Remove debris first

• Skim leaves and debris
• Vacuum settled dirt
• Clean skimmer baskets

Step 2: Test and adjust pH

Before stronger treatment, bring pH into an effective operating range. Chlorine works best when pH is controlled.

Step 3: Shock treatment + brushing

• Apply a chlorine shock based on actual pool volume
• Brush walls, steps, corners
• Keep filtration running

Step 4: Run filtration longer and clean the filter

• Extend filtration during recovery
• Backwash sand filters when pressure rises
• Clean cartridges as needed

Step 5: Clear dead algae (if water turns cloudy/gray)

After algae dies, water may look milky. You may need a clarifier/flocculant (depending on system) plus vacuuming.

Step 6: Stabilize and prevent recurrence

Once the water is clear:

• Maintain stable free chlorine
• Keep pH and alkalinity in range
• Adjust your routine for rainy season and heavy-use periods

Mistakes that make green water return

• Using only algaecide without restoring effective chlorine
• Skipping brushing
• Cutting filtration too much to “save power”
• Ignoring pH
• Using tablets continuously without monitoring stabilizer

Final recommendation

In Costa Rica, green water is rarely “random.” It’s usually ineffective chlorine + insufficient filtration + rain/organic load. The fastest way out is a structured diagnosis and a step-by-step recovery plan.