black spots

[justden]

I recently purchased a home with a indoor fiberglass pool that had been neglected for some time, here's my problem. The pool was very low on chlorine, the water was not very clear and most of the pool had a light brown stain on the fiberglass. After some research it was determined that I needed a two part product to remove the iron stain, two days later it was gone.
About a month later I started to notice some black spots on the walls and what looks like rust just below them and they can't be scrubed off. I am not sure if this had anything to do with it but two weeks before the black spots I added about 3000 gal. of well water, and the PH and alkalinity have been very high. Any idea what it is and how to get rid of it?
Next question, I have an automatic chlorine dispenser but I am using bromine tabs, can I use a chlorine test kit to check bromine/chlorine levels, when I try it the chlorine shows very high but when using a bromine test strip it shows low chlorine levels.

Thank you so much for any help you can give me,
Dennis

[chem geek]

From the use of well water and the high pH scenario, the spots are most certainly metal stains. A treatment with ascorbic acid should work to remove them (they are probably iron stains). See this post for info on how to remove metal stains and be sure and use the PolyQuat 60 algaecide as indicated since you will drop your chlorine to near-zero (the ascorbic acid won't work unless there is no chlorine).

Richard