Triple shock and brush immediately.

Yes, the fastest fix is a massive dose of liquid chlorine and elbow grease. The rain washed in algae spores and diluted your chlorine, so you need to hit hard.

First, skip the granular stuff—liquid chlorine works faster. Test the pH first (aim for 7.2-7.4 so chlorine works well), then add enough liquid shock to triple the recommended amount for your pool size. Brush every surface—walls, floor, steps—to break up the algae hiding spots.

Run the filter 24/7 and backwash when pressure rises. After a day, you should see the green start to fade to cloudy blue. Then floc or clarifier to settle the dead algae and vacuum to waste. It’s a few days of work, but way faster than waiting on algaecides.

Future you will appreciate the clean water, not the extra week of swamp.