A little about me I purchased a 1975 home about 9 months ago that came with an original pool. I am new to being a pool owner and have really appreciated all the great write-ups on this forum, I have defiantly learned a ton already. I am still learning for sure, some of the things I have done so far is the bucket test to see if I am leaking water which I am not just a lot of evaporation in the AZ sun. I have had my water tested and my CYA is well over 100 so I will be draining 75% of my pool in the next few weeks. At that time I will be sanding down what looks like calcium build up in my plaster they don't spread out they just grow taller and start out white and over time go brown b/c of dirt. If anyone has ever done this before a little do's and don'ts would be great. I will attach some pic's I took of the spots both the newer white ones and the darker one. I did do the chlorine tab test and nothing changed.