For heavy pool scale, muriatic acid. For light, a pumice stone.

Go with acid for stubborn scale, but start with a pumice stone if it’s thin.

If you’ve got hard water scale on your pool tile, muriatic acid (diluted 1:10 with water) is the go-to. Wet the tile first, apply with a sponge or sprayer, let it sit a minute, then scrub with a nylon brush. Rinse well. Don’t let it dry on the surface or it’ll etch.

For light, powdery scale, you can skip the acid entirely. A wet pumice stone (the real volcanic kind, not a fake one) rubbed gently over the tile will lift it off without chemicals. Test in an inconspicuous spot first — pumice can scratch softer tile like travertine or glazed ceramic.

If your scale is really thick, you may need an acid soak or even a specialty scale remover like Magic Lube or Scale Free. But muriatic is cheaper and works fast if you’re careful with dilution and PPE.

For pool plaster or fiberglass surfaces, don’t use acid — you’ll damage the finish. Try a phosphate-based cleaner or a mild vinegar soak instead.

Don’t skip gloves and goggles. Acid is not a toy.