I agree, the tin foil should go..... and the oscar, don't know what size tank he is in, but he needs atleast at a minimum 75G, but preferably 90G to 125G if your putting other fish, especially other NW cichlids with him.
Sorry to be one of those jerks that sits there and says that can't work but in your profie, it says your an animal lover, so if you want the best for them, either find a friend who has a bigger tank for both, or take them back to your lfs where maybe someone can come along and give them a bigger home.
EDIT: O, and too, your crayfish (if hasn't already) will def harrass you algae eater and snail, most likely end up eating them too. He might also cause some probs with your other fish....at night when they sleep, they will just drift in the tank, and seeing how most crustaceans hunt/'forage' at night, he will most likely cause damage to the other fish, even if he is way too small to eat them. So, i would get rid of the crayfish in that tank if you wish to keep your other fish healthy. You can just put him in a 10G by himself and he will be more than happy
