Join Date: Aug 2011
Location: State of Emergency
Not sure why h2o2 killed it.
Anyway, I've used cups and cups of h2o2 in a 20 gallon before and never had ill effects other than some clouding.
I read on this forum about someone using it and then losing a fish, but the fish was old, and I don't believe it was related, although the owner certainly did.
If you're spot treating, be sure to turn of the filter.