Muriatic acid is the best bet for pool scale.

Yes, but you have to be careful with it. Muriatic acid (diluted hydrochloric acid) is the standard for removing calcium carbonate scale from tile. It’s cheap, fast, and works better than most off-the-shelf “scale removers.”

Here’s the deal: you don’t just pour it straight. Wear gloves and goggles, dilute it per the bottle instructions (usually 1:10 with water), apply with a stiff brush or sprayer, let it sit for a minute, then scrub and rinse thoroughly. Don’t let it dry on the tile or it’ll etch grout and burn your skin.

For light scale, a pumice stone wetted with water or a mild acid cleaner works too — but muriatic is the nuclear option that actually finishes the job. Just never mix it with bleach or anything containing chlorine. That makes toxic gas.

Future You’s lungs will thank you for the PPE.