Shock the pool and raise the pH.

Test the water first, then you’ll likely need to shock and raise the pH.

Heavy rain does two things: it dilutes your pool chemicals and drops your pH (rain is slightly acidic). Your chlorine level will be low, alkalinity may have fallen, and the water might look cloudy or greenish from debris runoff. Don’t just add shock and hope — test the pH, alkalinity, and chlorine.

In practice, you’ll usually add a shock treatment (calcium hypochlorite or a non-chlorine shock) to