Potassium Permanganate & the Biofilter

One of my Goldfish has a white bump on his nose and it's getting bigger. It
doesn't seem to have them anywhere else on it's body and none of the other
fish seem affected. I think it's fungus, but I'm not sure. I was going to
treat the tank with PP, as it's a pain to move him because of his size. So I
was wondering if the PP dose at 2 PPM will kill my biofilter? I was
considering turning off one of the filters for an hour (max) until the PP
had diminished somewhat and then restarting it before the bacteria died of
oxygen starvation.

TIA