I have never had peroxide do this but anything is possible. Ok, its time for meds. Im sure you have a petsmart near you. I would give maracyn 2 (not regular maracyn) a try. Your other guys will be fine with the meds even though they dont need them. Be prepared to do atleast 2 full courses of the maracyn2 to get this under control. If you have any carbon in your filters, remove it before starting treatment. Also, keep an eye on your water parameters during treatment. You will need to do a few big water changes to remove the pimafix (or was it melafix?) from the water. I would suspect this product may be a factor here. Keep us posted!