What is wrong with my Betta now?

k i have a Betta fish and he was doing fine before i changed his water and i accidentally torn his fin a tinny bit when i was trying to take him out so i clean his tank and i decide to put melafix in the tank to fix the tear.but he does not like the melafix it makes him look lethargic. so the next day i clean the tank again and i did not put melafix in the tank and and when i got done i put him in the new clean water and he is still acting lethargic so i don't know what to do. i am at wits ends