Foamy pool water is a chemistry problem, not a mystery.

Chemical imbalance — usually too much algaecide, high calcium hardness, or a phosphate overload.

Most foam comes from overdoing the algaecide. The non-foaming kind exists for a reason, but if you already used the regular stuff, a little shock usually clears it up. High calcium hardness (above 400 ppm) can also cause foaming, especially if you’ve got a lot of aeration from fountains or splashing. Phosphates from leaves or fertilizers feed algae, and when they die from chlorination, the dead cells create foam.

Fix it by testing your water first. Then shock the pool to break down organic residue. If that doesn’t work, check calcium and phosphate levels and adjust. A pool defoamer (a silicone-based product) will knock foam down in minutes, but it’s a bandaid — address the root cause or it’ll just come back.

The actual solution is boring: balanced water chemistry. Keep your alkalinity, pH, and sanitizer in range and foam is rare.