From all that I have heard it is safe. Ottos might be sensitive, so if you have those fish, just do a half dose. I want to give it a try too, but I am not sure if it will kill my beneficial bacteria in my filter. I would hate to have to recycle my aquarium. :shock:
Finally, in the discussions on Potassium permanganate at SimplyDiscus, there was some talk about H2O2, again mostly as an end to PP treatments. http://www.simplydiscus.com/forum/ The talk about possible pH changes was from there.
why did you even want to use this in a discus tank?
From what i understand the use of H2O2 from the book of Aquarium Fish Disease, and one of the Amano's books that given a small dosage of H2O2 will dramatically increase the oxygen level, and this will affect the algae, hence kill them.
If high enough dosage is given, I am sure it will affect the bacteria in filter, but if you're worried about that, just turn off the filter for a hour or two, with the light on, H2O2 will turn into oxygen and water very quickly. I would also house the fish somewhere else during treatment if I plan to use high dosage.
I've never tried it with discus however at the concentrations I've used in the past it has never hurt any fish. My biological filters also survived these concentrations quite well however turning them off and using a powerhead for circulation during treatment is probably a wise idea.