What's the best way to remove scale from pool tile?

Muriatic acid is your best bet, but dilute it (1 part acid to 10 parts water) and work in small sections with a stiff nylon brush. Rinse immediately—never let it dry on the tile. For light deposits, use a wet pumice stone gently. Avoid metal scrapers. Wear gloves, goggles, and old clothes; test a hidden spot first. For stubborn scale, a commercial remover like Scale Free is safer and works just as well.