So over the last week I noticed lots of small spots on bottom of pool that look like rust. I did the Vitamin C test (used tablet dissolved above stain and several in a sock) but stains were not removed. I used a small sponge and scrubbing them got stain out, but only on smooth part of fiberglass pool not the textured areas on bottom.
Reading around the site, I came to conclusion it may be cobalt spotting especially since my Calcium is really low. I took my water to local pool store and here are my water chemistry numbers:
No iron or copper detected.
I will try and take some underwater pictures later today, but wanted to get people's opinion, before I go buy and add calcium chloride dihydrate to raise it from 40 to around 250. Is that the right first step? Will this make these stains go away or just prevent from getting more?