Pool tile guide What's that white crust on my pool tile?

It's minerals left behind by the water

Tap water carries dissolved calcium and other minerals. Every time your pool loses water to evaporation, the water leaves but the minerals stay. Over time the remaining water gets more concentrated, and minerals come out of solution right where the water dries: at the tile line.

Splashing and spillovers make it worse. A raised spa wall or waterfall is wet and dry over and over, so it often builds the thickest crust on the pool.

Calcium carbonate vs. calcium silicate

Calcium carbonate is the common white, flaky kind. It's newer and softer, and some of it can come off with regular brushing.

Calcium silicate is grayer, harder and smoother, and it's bonded tightly to the tile. It usually means the buildup has been there for years. Brushing won't touch it.

Why some pools get it worse

Hard source water, especially well water, a pool that's topped off often, high pH or high calcium hardness, and a water level that goes up and down all speed it up. In the Houston area, pools on groundwater tend to scale faster than pools on mostly lake water. See Houston hard water and your pool.

Getting rid of it

Light carbonate can be kept in check with weekly brushing. Set-in scale needs professional tile cleaning by bead or media blasting. The water is lowered about 6 to 12 inches, and the pool is never drained.