I have a 20 gallon tank with s small convict fish. I bought a huge tank as my project tank and there was a convict in it with no filter system and it was only a few inches deep. I had to save the little fella so I put him in my 20 gallon. It was cycled and ready. I just live a long way from a pet store and was waiting. Anyhow, the tank has algae growing. I tried putting a snail in to help (on the advice from the owner of the pet store) and he ate it rather quickly. I feel so bad for the poor guy but didn't even know until I looked and there was an empty shell in a short time. I am worried about putting anything in with him. What can survive in a tank with this guy?