How Much Chlorine Does It Take to Fix a Green Pool?
Algae consumes chlorine fast — you need to "pay off" its chlorine debt before any residual sanitizer is left to clear the water. Light green/cloudy needs roughly 2-3x a standard shock dose; dark green needs 4-6x; black/very dark green often needs multiple treatments plus brushing and algaecide.
Process: test what you can, brush the pool first so chlorine reaches the algae, shock aggressively at dusk/night (UV burns off chlorine fast), run the pump continuously, retest and repeat if needed (often 2-3 rounds), filter continuously as algae dies, then vacuum the dead algae once visible.
Under-shocking wastes a day waiting for nothing; over-shocking wastes chemical and can throw off other chemistry. Pool Balance's free calculator calculates the exact pounds or gallons of shock needed for your pool size and how green the water is.