While swimming the other day in my 4 y/o gunite pool, I noticed that one one section of the pool the top row of tiles (we have two rows of 2x2 tiles) appear to be lifting away from the wall. I am meticulous with the pool and keep a pump in during the winter to keep the water level low. Any idea what's happening????? Am I going to have to retile? Of course we are 1 yr out of warranty!