the only reason they put the lable of for tropical fresh water fish is to let you know 2 things that it is unsafe for salt water fish and unsafe for food fish as it can cause harm to humans. you shuld be fine to treat with that but if you read the ingreadiance and it says malacite green dont use it on cats it is realy nasty. i use copersafe by mardel or are you talking about internal parasites?