I received a huge 6.8 oz can of flake food from a relative. It's Wardley's Tropical Flakes, purchased from Meijer. I have no idea how old it is. It is almost full. The LFS sold me a 1 oz can of TetraMin. They look pretty much the same. Does it matter what kind I give the fish? Does the old food go bad (it looks okay)? Is one kind of flake food better than another?