I have some Wardley Ickaway which i must have bought about 3 years ago. it doesn't have an expiry date. can anyone tell me if it would still work? i'm a bit worried about on of my corys and i'd feel better once i'd treated the tank with something. the only other med i have is melafix which i think isn't safe for corys? i've used the ickaway before with corys (half dose i think) and it worked fine.