What is This (Picture)?

[Seahunt]

What is this? It showed up again this year. I believe it started below the water line but it is now above it. I have several spots. I raised my Calcium Hardness from 170 to 270 when it first started showing up. Don't know if that is the right thing to do. Any advice would be appreciated.

http://i49.photobucket.com/albums/f285/schmity1/tile.jpg

[geeman]

could be efflorescence which is usually a sign of loose tile or coping. try running the head of a hammer over the top of the coping and over the tile. listen for a hollow sound. if it sounds hollow its loose tile. the deposit will continue to show up until the tile is replaced. If its not loose try cleaning it with a light acid solution and a rag.

[Seahunt]

Thanks Geeman. I googled it and I guess there is nothing a consumer can do to fix or prevent it. Thanks again,

Matt

[Surface-Renewal]

If there is a planter just behind the pool wall it probably is leech. There is a way to combat it.
First, when most pools are gunited, the gunite is shot against dirt, especially when the pool is in confined spaces. Realistically, the pool should be shot against a form, the form then stripped, and finally waterproofed on all pool walls that will house a planter or at the least a drain pipe installed. Most likely water from irrigation sprinklers has traveled through the ground picked up minerals along the way, and deposits them on the surface much like a cave makes stalactites. So to fix it, remove the dirt behind the pool wall to below the water line, pressure wash the gunite clean. Wait for it to thoroughly dry and apply Henry's waterproofing to the backside. Allow to cure, and back fill. Your problem should be fixed. More info PoolTileCleaningPro.