Why Is My Pool Green? Causes and How to Fix It

You pull the cover off, or come back from a week away, and the water has gone from clear to green. It's alarming, but it's also one of the most common and most fixable pool problems there is. Here's what causes it and how it gets solved.

Green water is algae

That green tint is an algae bloom. Algae spores are constantly entering your pool — on the wind, on swimsuits, in rainwater. They're harmless in small numbers because sanitizer kills them off. Water turns green when the sanitizer loses that fight.

What lets algae take over

Low or exhausted chlorine. The most common cause by far. Chlorine gets consumed by sunlight, heat, debris, and swimmers. Once it drops too low, algae multiply fast — often overnight.

Unbalanced water. If pH is too high, chlorine becomes far less effective even when the level reads fine. Chemistry has to be right for sanitizer to work.

Poor circulation or filtration. Water that isn't moving and filtering enough gives algae quiet corners to establish. A dirty filter or too-short pump run time both contribute.

Heat and sun. Hot, sunny stretches burn off chlorine faster and speed algae growth.

Debris. Leaves and organic matter feed algae and consume sanitizer as they break down.

How it gets fixed

Clearing a green pool follows a reliable sequence: test the water, then brush the walls and floor thoroughly to break algae loose from surfaces. Shock the pool with a strong dose of sanitizer, run the filter continuously, and clean or backwash the filter as it loads up with dead algae. Add algaecide as appropriate, then rebalance the chemistry. The water typically goes green, then cloudy, then clear over a few days — cloudy is progress, not failure.

Keeping it from coming back

Consistency is the whole game: maintain sanitizer levels, keep pH in range, run the pump long enough each day, keep the filter clean, and brush regularly. That's exactly what a weekly service does — the reason regularly serviced pools rarely go green is that nothing is ever allowed to slip long enough for algae to gain a foothold.

When to call for help

If you've shocked the pool and it's still green after several days, if the water is so dark you can't see the bottom, or if you'd simply rather not fight it — that's a good time to bring in a pro. Severe blooms sometimes need multiple treatments and a filter deep-clean.

Dealing with a green pool in Carson City? Call (775) 306-3454 — we'll get it clear and keep it that way.