A green pool is an algae bloom that out-ran your chlorine — and the fix is the same order every time. Here’s what turned it green, how to tell which algae you’ve got, and the step-by-step plan that takes it back to blue.
Green water isn’t a mystery. It’s algae that bloomed the moment your sanitizer slipped — and in Florida, it gets a lot of help.
Green is algae winning. The moment free chlorine dips — a hot week, a busy weekend, a stabilizer that got too high — algae spores already in the water start multiplying faster than the chlorine left can kill them.
Algae doubles fast. A pool that looked a little dull on Friday can be full-on green by Sunday. That speed is why "I’ll deal with it next week" almost never works — you have to hit it hard and early.
Our heat speeds algae up and burns chlorine off; summer storms dump acidic rain that drops your pH and dilutes your sanitizer, then wash phosphate-rich runoff in to feed the bloom. Green-after-a-storm is a Tampa Bay classic.
Which algae you’ve got decides how hard you have to hit it — and whether a single shock will do it or you’re in for a few rounds.
Bright green, slimy, free-floating or clinging to walls and steps. It clouds the whole pool and it’s the easiest to kill — a proper shock and good filtration usually clears it in a day or two.
Looks like pollen, sand, or dirt dusted on the floor and shady walls — and brushes away then comes right back. It’s chlorine-resistant, so it needs a much harder, repeated shock to truly clear.
Dark blue-green spots with roots that dig into plaster and grout. The toughest of the three: it has to be scrubbed open and spot-treated, or it keeps coming back from the same spots no matter how much you shock.
Green-tinted but clear (not cloudy) water is often dissolved metals — usually copper from fill water or an off pH — not algae. Yellow “dust” can just be pollen. The fix is completely different, so it’s worth confirming before you dump in shock.
Most pools that “won’t clear” got tripped up by one of these. Get the order right and the same chemicals do the job in a fraction of the time.
Five steps, every time. Do them in this order and most green pools are blue again inside a couple of days.
Chlorine barely works above pH 7.8, so we test and bring pH and alkalinity into range before shocking. Skip this and most of the shock you add is wasted.
Walls, floor, steps, and the shady corners where algae hides. Brushing breaks the protective layer so the chlorine can actually reach and kill it.
We shock to a high free-chlorine level, dosed to how green it is (double or triple a normal dose), after sundown so the sun doesn’t burn it off. Mustard and black algae get repeat doses.
As the algae dies it turns gray and cloudy — that haze is the filter’s job. We run the pump non-stop and backwash or clean the filter as it loads up with dead algae.
A clarifier or floc gathers the fine dead algae so we can vacuum it out, then we retest and rebalance chlorine, pH, and stabilizer so the water comes back swim-ready — not just clear.
A pool that goes green again and again has an underlying driver. These two are the usual suspects — worth ruling out before the next bloom.
The questions homeowners ask most about a green pool. See all FAQs →
A normal green-algae pool usually clears in 24–48 hours once you balance, shock hard, and run the filter non-stop. A deep green, or stubborn mustard or black algae, can take three to five days and more than one shock.
No. Green water means algae and bacteria are thriving and your sanitizer is overwhelmed, plus you can’t see the bottom — which is a real drowning hazard. Wait until the water is clear and chlorine has settled back to a normal 1–4 ppm.
Heavy Florida rain is mildly acidic, so it drops your pH and dilutes your chlorine, while runoff washes in phosphates and debris that feed algae. With our heat, that combination can turn a pool green within a day. Test and re-shock after any big storm.
Algaecide is a preventer, not a cure for a full bloom. To clear a green pool you need chlorine to actually kill the algae — shock is what does that. Algaecide is best used afterward to help keep it from coming back.
A pool that goes green again and again almost always has an underlying driver: high cyanuric acid (stabilizer) locking up your chlorine, or nitrates and phosphates feeding the algae faster than you can sanitize. Until that root cause is fixed, you’re treating the symptom.
We clear green pools across St. Petersburg and the Tampa Bay area — and keep them blue with weekly service for one flat rate.