Maybe this will help?
What causes calcium deposits on swimming pool tile

Calcium is part of water. Like rice is white and water is wet. Not much can be done about calcium build up. There are some suggestions that I give my customers but they do take a big commitment.

Being that the calcium is on the tile the first thing is for us to clean the tile, then seal the tile. This helps prevent the calcium build directly on the tile and makes cleaning it off easier.

I would also suggest clients go out daily and brush their tile. This will help with the build up as well.

Lastly, use a calcium preventative called Scale Tec. This helps prevent the calicum build up or at least slows it down.

These are the best solutions/practices I can suggest, however calcium is part of water. These methods will help minimize the build up but because water is not purified, calcium comes with adding water to the pool.

Are you certain it is scale from your pool water? It may be efflorescence coming from your tile grout. If that's the case, there's not much you can do. Prior to the tile installation a waterproofing material, such as Thoroseal, should have been applied to the pool surface to limit this. The tile grout also needs an additive as well such as Acrylic 60. Efflorescence is a naturally occurring process and it produces a white scale. It's not limited to swimming pools. It's seen commonly seen on most masonry walls and stonework.

If the scale is developing from your pool water, a periodic light solution of acid and water will help. If your calcium levels are above 300 ppm, this will be concurring problem. There is no chemical to reduce the calcium levels. Draining and refilling a pool is only way to reduce calcium levels. It's a Catch 22 though if your fill source is high in calcium. There are good sequestrian agents such as Jack's Magic that control scale. Used on a weekly basis it will work well.