My brother in law turned off his tank and was letting all the fish die. I tried to save but most died but an algae eater. Fish now has what looks like a sore on his back. What do I do? I don't know about testing or anything else. He is in small 1 gallon tank with air and heater and that is it. I don't know anyone who has a tank who can take him and save. I don't want him to die if possible. Thanks!