Evan,
That is what I thought, I used floc about 6 years ago I wwas using baquacil and decided to switch to chlorine. The pool company closed my pool for the winter only putting in algacide and baquacil shock. When they opened the pool in the spring they put in chlorine - what a mess! They didn't know what happened - the water turned a florecent green - then they threw in a bunch of calcium, cya, and kept shocking the pool. Needless to say I ended up with a milky green pool! The water was so unbalanced that I had to drain about 1/2 the water out and start over. When I did get the water cleared up there were brown stains all over it. That's when I decided to do the chemicals myself. I got the stains out, and then put n floc. I didn't get the stains back for the rest of that year. Unfortuanately the next year I got stains again, got rid of them, but didn't use floc. I did get some back. I have not used floc since, but I was thinking after you said that the metals can't be filtered out maybe if they could be somehow made heavier than the water by binding onto something, they could then be filtered out. I still don't know where my metal comes from in my pool. The only thing I can think of is my heater, I think it may be put in after the pump. My well water doesn't test that it has iron, but I do have hard water. I found this website three years ago and I have learned so much.. But I still don't know what is causing my stains, just how to get rid of them. If you think of anything please let me know. I don't worry about the stains since I can get rid of them, but it is driving me crazy trying to figure out where they are coming from, and if the metal can be filtered out of the water once it is back in suspension.