A pumice stone and white vinegar will remove pool tile scale without damage.

Use them together. Wet the pumice stone first (always wet – prevents scratching), dip it in white vinegar, and gently rub the scale. The vinegar softens the calcium, the stone buffs it off without gouging the tile.

Avoid wire brushes or steel wool – they scratch glazed tile and destroy grout. Muriatic acid works but is easy to overdo; one wrong splash and your grout is pitted. Vinegar is weaker but safer for regular maintenance.

If the scale is really thick, let a vinegar-soaked cloth sit on it for 15 minutes before scrubbing.

The key is patience, not elbow grease.