i recently moved my SMB into his new 120g hopefully permanent home, although some day i may want to go bigger, and do not know what to do with the smaller 20g tank that is now sitting empty.... any thoughts? i want thinking just keeping the feeder fish i buy for him in it and selectively feeding him, but we want the SMB to get pretty big and just put a water heater in there to slightly increase the water temp. so he eats more. i was thinking maybe going saltwater but i heard its a pain in the butt to get started and what tropical fish could i keep in 20g?