My aquarium has had a bacterialdisease, killing all but one fish, who is in her quarantine bucket. When and how can I put the fish back into my aquarium and make sure that she doesn't just become sick again?
Most bacterial infections are omnipresent bacteria, that are always there and usually just opportunistically use a bad immune system to infect fish. So there is no way of removing them. Instead the fish has to be brought to a better health, with optimal conditions and maybe vitamin supplements to the food, then the bacteria should not bother it anymore.