I bought a house with a plaster pool that had large and small raised spots all over the bottom, and I had a company remove all the plaster down to the gunnite, then re-plaster with new tile. After 2 years I seen two raised spots starting to come back. they start small, and get larger / wider over time. I drained the pool, touched them up with pumas stone, then acid washed. Now after 3 years I have 4 or 5 large 2 inch round spots and 100 small raised spots on the bottom of the pool. after pumas stone and brushing the pool the large spots are no longer just raised , but both raised and indented. At this point I am not sure what to do, I was thinking sanding and painted, but lots of people say don't paint. What's the best approach to fix this plaster ? Am I required to re-plaster every 3 years or so ?