thanks for the response,
on city water. no pool test for iron or copper. I'm not sure what a mineral system is, so i'd have to say no. I never added copper algaecide, but can't confirm it was never added before I took over this pool.
I'll try the vitamin C/trichlor. I feel like the vitamin C thing hasn't worked for me before. I have a bad spot in my current pool that is from a construction staple falling in the pool and resting on the bottom. I let that sit with vitamin C and scrubbed it and and rubbed it and it did not alter it at all. so I know that was from metal, and vitamin C didn't move it...I'll give the vitamin C vs trichlor puck tomorrow, but is it possible that vitamin C would have no effect on a known metal stain?