Wait at least 15 minutes — but check the label.

Yes, for most standard pool algaecides, 15-30 minutes is fine. The chemical disperses quickly and dilutes to safe levels fast. If you’re using a concentrated or heavy-duty algaecide, the bottle will say — some recommend 24 hours. Read the label. That’s not optional.

The bigger risk is not waiting long enough for the water to circulate. Turn the pump on, give it 15 minutes, then swim. If you added chlorine or a shock treatment at the same time, that changes the math — you’ll want to wait until chlorine levels drop to 1–3 ppm.

If you can’t find the label and you’re guessing, play it safe: wait an hour. But honestly, 15 minutes is standard for algaecide alone.