Rain doesn't turn pools green — phosphates do.

Phosphates in the rainwater feed the algae that turn your pool green.

The rain itself isn’t the problem. It’s what the rain brings with it — dust, pollen, bird droppings, lawn fertilizer runoff, and other organic junk that landed on your deck or roof. All of that is loaded with phosphates and nitrates, which are basically algae fertilizer.

Meanwhile, the rain also dilutes your chlorine level. So you’ve given algae a feast and then fired the bouncer. No surprise the pool turns green within 24–48 hours.

The fix isn’t complicated: test your phosphate level (most pool stores do it for free), use a phosphate remover, and shock the pool hard. If you just add chlorine, you’ll burn through it faster than normal because the phosphates are still there to feed new algae.

Testing for phosphates after a storm is smarter than just adding more chlorine.