Just finished my Pool Opening SLAM and the pool looks great for the most part. There are a couple of black marks on the fiberglass that almost look like burns. Since I am about to do a AA treatment I took a little AA and rubbed it on one of the marks and after a little elbow grease it fades away. I wasn't doing the AA for these marks just a couple of others, but hey if these get lifted to then great! I have a couple of these around the top half of the pool (on the fiberglass) and usually right in the center of a welt. A welt as in a bubble like shape forming on the 30 Yr old fiberglass. Any ideas as to what is happening? Seems like there are more then last year.
Last Night Test Results
Here are a few pictures.