Shock it as soon as the rain stops — but test first.

Yes, but you need to do it right.

Rain dilutes chlorine, muddies the water, and can drop your pH. So before you dump in a bag of shock, grab a test kit. Adjust pH to 7.2–7.4 first — shock works best there. Then use a non-stabilized chlorine like calcium hypochlorite. If the water looks cloudy or you had a big storm, double the dose.

Don’t bother with algaecide unless you actually see algae starting. Run the pump overnight and brush the walls the next morning.

Future you wants clear water, not a science experiment.