Shock before the storm.

Yes, there’s a specific routine. Test and balance your water chemistry before the rain hits, then run the pump for a few extra hours.

Heavy rain does two things: dilutes your sanitizer and drops your pH, and washes in phosphates, nitrates, and algae spores from the air and yard. If your chlorine and alkalinity are already low, that’s like a welcome mat for algae.

The fix isn’t complicated. A day before expected rain, check your chlorine and pH. Bring chlorine up to the high end of normal (around 3-5 ppm for most pools). If you use stabilizer, check that too. After the rain, test again and shock if needed. A phosphate remover now and then helps, too, but it’s not the daily battle.

Don’t skip running the pump during or right after the rain. Water circulation stops algae from settling.

This is one of those “ounce of prevention” things. Do the work before the clouds show up, and you’ll skip the green mess.