Wait 20 minutes after adding algaecide. Or just follow the label.

Yes, it’s generally safe after about 20 minutes—but read the bottle first.

Most liquid algaecides are designed to disperse quickly. If your pump is running and the water is circulating, 15–30 minutes is plenty for the concentration to drop to safe levels. The risk isn’t the algaecide itself (it’s not super toxic at pool doses), but the fact that it’s concentrated right where you pour it. Give it time to mix.

Some copper-based or “quat” algaecides recommend longer waits, like 24 hours, especially if the label says so. That’s usually because they’re more aggressive or stain-prone, not because they’ll hurt you instantly. But follow the label—it’s not just lawyer stuff.

If you’re unsure, wait an hour. Nobody got hurt by waiting too long.