My fiberglass pool has been installed for about 4 months now. I have a SWG and a sand filter. The water is crystal clear and the parameters have been where they are supposed to be. When the weather turned cold, I noticed these two dark blotches on the bottom. I cannot tell if the dark area or the light area is the original color of the pool. I tried the ascorbic acid on both areas with no success. I use municipal water and added the Jacks Purple Stuff when the pool was filled. Has anyone experienced this and what are my options?
Here is a link to the photos. There is water in the pool.