Over the winter, I bought a house with a gunite pool w/ spa. It was built in 2003. I opened it up last week and went through the normal process of cleaning up the water. Now that the water is clear, I've noticed the plaster is worn, but not knowing much about pools I don't know how bad. What do you guys think? Take a look at the pics I've attached. What is this caused by? Will I need to get the plaster replaced soon?