Shock it. With chlorine, after you test.

Yes, heavy rain dilutes your chlorine, drops the stabilizer, and dumps in algae food. If you don’t shock, you’re rolling out the green welcome mat.

First, test your water. Rain usually raises pH and lowers chlorine. If pH is above 7.6, bring it down before shocking — chlorine works best below that. Then add enough shock to reach a breakpoint level (usually 10-15 ppm depending on your pool size and stabilizer). Use a calcium hypochlorite shock or a dichlor if you need stabilizer too.

Run the pump overnight. Brush the walls and floor the next morning. Don’t swim until chlorine drops to 1-3 ppm.

One tip: keep a bottle of non-chlorine shock on hand for post-storm days when you just want to oxidize contaminants without the heavy chlorine swing. But for preventing an actual bloom after a downpour? Chlorine shock is the way.

Your pool will thank you by not turning into a swamp.