I did not cover by pool this winter. It's a new pool so this is the first winter. Did winterize and dropped the water just slightly below by baja shelf. During the course of this winter, as I have gone in to scoop out some debris, I have noticed that in my shelf area the diamond brite appears to be spalling like concrete would and if if run my hand accross it I notice lots of bluish debris. Any thoughts on why this is happening and what can be done?