Preventing ulcers

While some types of bacteria (and viruses) can cause ulcers in perfectly healthy fish, often their appearance is a sign that the fish is stressed for some reason or has incurred a skin injury.

Always consider possible underlying risk factors, such as poor aquarium hygiene; incorrect water conditions for the fish species in question; attack/bullying by other fish; physical injuries such as skin abrasion on rocks; skin damage caused by skin parasites such as Ich or velvet. If there is an underlying cause, even effective treatments may not work — and in some cases, simply by identifying and eliminating the source of any stress, the ulcer may heal by itself.