Rainwater feeds algae. Shock it hard.

Yes, rain can turn your pool green. It’s not magic—it’s a perfect storm.

Rain brings in dust, pollen, and other organic junk. That’s food for algae. It also dilutes your chlorine and can knock pH out of whack. And if you got enough rain to overflow, it probably stirred up whatever spores were lounging in the corners.

Fix it by shocking aggressively. Use enough chlorine to get past the “breakpoint” — usually 10-15 ppm for a normal green bloom. Brush the walls and floor to break up any clinging algae. Run your pump 24/7 for a day or two. Then test pH and alkalinity once the chlorine comes back down.

Don’t bother with algaecide until after you shock. Chlorine is the hammer. Algaecide is the touch-up.