Ok. For the Pebble Tec experts. I built my own pool back in 2002. The finish I chose was Black Pebble Tec. I have not been the best at maintaining water quality. The pool still looks great. I do have some areas of white spots. The other day I put a chlorine tab in the spa and noticed where it dissolved the surface darkened to what appears to be original color. Question is what happened? And is there something I can do to make entire surface look this way short of draining and acid washing?