How long should I wait after adding algaecide before swimming?

Wait about 20 minutes if your pump is running and water is circulating, but always follow the label first. Most liquid algaecides disperse quickly, so 15–30 minutes is enough for safe concentration levels. Some copper-based or “quat” algaecides may recommend longer waits like 24 hours—follow the label. If unsure, waiting an hour is safe.