I'm in the middle of my 1st time SLAM and I'm seeing these tiny brown "dots" appear on the bottom of the pool in a few locations. I can't take a picture because it's dark outside, but they are 4-6cm groupings of tiny (approx. 1 millimeter) dots. They are stuck hard to the pool and are bumpy and hard and won't come off with brushing. If I work at it I can scrape a few off the bottom with my fingernail. They come off and I can hold them in my hand and are like tiny brown bumps. What is this? I can't think of any kind of algae that would behave this way. I'm wondering if this is some form of iron? We filled our pool with well water and we've had periods of high iron. Last year (our first year) I did a terrible job at keeping high FC, so this is the first time my pool is having a high FC level. My water is perfectly clear, though, and always has been... any ideas?? I'll post a picture tomorrow when it's light outside.
Current pool level (mid-SLAM)