I was just given one of those small acrylic terraniums which used to house crickets for a frog. After a good wash with vinager, I am sure it will be safe for fish. I would like to set it up as a small coldwater tank for my desk. It will have a whisper 10 filter as I have one of those lying around the house. It will use an aquaclear sponge for mechanical and biological filtration as I don't see it neccessary to go and buy expensive cartridges just to get activated carbon. Any good coldwater fish that I could possibly put into this small approximately 3 gallon container? The room temperature will be about 72* F