Used peroxide many times in many tanks and never
had a problem.
I've never heard of using peroxide as a tank treatment. I'll have to
put that on the list of things to research some time.
Looking through the tank from one end to the other
the far wall is RED and I mean RED!
Did you happen to use any Tetracycline on it? I've found that
Tetracycline treatments turn my tank a vivid red color. Water changes
and fresh carbon in the filter has taken care of the problem for me.