Pumice stone is your best bet for calcium scale.

Yes, but you need to be gentle and use the right tool.

A wet pumice stone is the standard for ceramic or porcelain pool tile. Wet the stone and the tile, then rub lightly. The stone is soft enough that it won’t scratch the glaze, but the scale will come off. Rinse frequently and stop if you see any wear on the tile.

Do not use a wire brush, steel wool, or any abrasive pad. Those will scratch the glazed surface and make scale stick even worse next time.

If the scale is really thick, a diluted muriatic acid solution (10:1 water to acid) can help, but you need to neutralize it and rinse thoroughly. Acid is risky for grout and metal fittings, so only go there if pumice doesn’t cut it.

Test in an inconspicuous spot before going all in.