Chemically Remove Stains
Drain the pool. Wipe any visible algae from the tile before chemically removing the stains.
Put on the rubber gloves, safety glasses and face mask to protect your skin and lungs before you use chemicals to clean the tiles. Muriatic acid is a corrosive acid that effectively removes stains from tile, stone and concrete surfaces.
Dilute muriatic acid with water using a 1-to-1 ratio. Fill a bucket with a gallon of water and add a gallon of acid to the water. Pour some of the solution into a clean plastic spray bottle.
Spray the solution directly over the hard water stains. Scrub the stains with the soft bristle scrub brush. Use a soft bristle brush to help prevent scratching the pool tile.
Rinse the solution away with a garden hose immediately after each application. Wipe the tiles with clean cloths.
Naturally Remove Stains
Combine 2 cups white distilled vinegar and 1/2 cup baking soda in a bucket. The combination of acetic vinegar and the base baking soda will produce a chemical reaction that causes the mixture to bubble.
Soak a clean cloth in the mixture and rub it onto the hard water stains. Let it sit for 15 to 20 minutes.
Gather the vinegar and baking soda solution onto a soft bristle scrub brush. Scrub the tiles with the brush to remove the stains. Use a little elbow grease, but be careful not to scratch the tiles.
Fill a bucket with warm water and pour the water over the tiles to rinse the cleaning solution away.
Inspect the tiles for any remaining hard water spots. Repeat the process if there are stains left on the tile. Difficult or set-in stains may require two to three applications to remove the stains completely.