Why Does My Pool Turn Green After It Rains?

Houston rain can change more than the water level.

Your pool looked great yesterday.

Then a Houston rainstorm rolled through, and suddenly the water doesn't look quite as inviting. Maybe it's slightly cloudy. Maybe there's a green tint developing. Or perhaps the pool looks fine, but the chlorine reading has dropped dramatically.

What happened?

Rainwater itself isn't necessarily the problem. It's everything that comes with it.

A heavy rain can introduce leaves, pollen, dirt, organic debris, and other contaminants into the pool. Water running across the deck or surrounding landscaping may carry even more material with it. At the same time, several inches of rain can dilute the pool's carefully balanced chemistry.

Then the sun comes back out.

With September temperatures still reaching into the 90s in Houston, warm water and strong sunlight can create excellent conditions for algae growth—especially if the pool's sanitizer level was already on the low side before the storm.

That's why a pool can seem to change almost overnight.

After significant rainfall, start by removing leaves and other debris from the water and skimmer baskets. Check the water level, particularly if the pool became unusually full, and test the chemistry rather than assuming everything remained balanced through the storm.

Pay particular attention to sanitizer and pH levels. Rain and debris can increase the demand on your pool's sanitizer, while changes in water chemistry can affect how efficiently that sanitizer works.

It's also important to keep the circulation and filtration systems doing their jobs. A pool that's been hit with a large amount of debris may require more attention to skimmer baskets, filters, and circulation than it does during a stretch of clear weather.

And don't assume that clear water means nothing changed. Chemistry can move out of balance before the water begins looking cloudy or green. Checking it after a substantial storm gives you a chance to make smaller corrections before you're dealing with an algae problem.

September in Houston isn't really fall pool season. It's still swimming season—with a little more rain thrown into the mix.

Keeping an eye on your water after those rainy days can help make sure your pool is ready when the sun inevitably comes back out.