Calcium stains, sometimes called scale, occur around the top edge of a pool and look like white or gray crusty deposits. They are often caused either by hard water or by minerals that seep out of nearby tile mortar. If left in place, they may result in permanent stains on the tile as well as causing the pool to look dirty and unattractive. Removing the calcium deposits from pool tiles will require some physical labor. Unfortunately, you'll have to repeat the process periodically, since the stains often return.
Drain the water in the pool by at least 6 to 10 inches so that you can easily access the calcium-stained areas. This also allows you to wipe the loosened calcium off without depositing it into the pool water.
Kneel down on the edge of the pool, or get into the pool if you don't mind getting wet. Place a stiff-bristled tile brush on top of the calcium deposits and scrub the pool tiles using circular motions to loosen the deposits.
Wipe the pool tile with a cloth or a paper towel to remove the loosened calcium. Examine the area to see if all of the deposit came off, and use a pumice stone to gently scrub in circular motions if any calcium remains.
Remove thick scale from the tile using a razor-blade scraper, being careful to maintain a low angle and avoid scratching the surface.
Wipe the area again with the cloth. Repeat the process to clean around the perimeter of the pool to remove the remaining calcium deposits.