i actually had a 2.5 gallon that was absolutely gorgeous that i messed with maybe once every two weeks. i had a large number of zoo's, some acans, a boxer crab, and a yellow rose goby. everything worked awesomely until it fell off the wall while i was on vacation and was completely dry by the time i came home. needless to say it was a complete loss. the only circulation/ filtration was a hagen mini submersible filter/ powerhead, and quite a bit of macroalgae and a mangrove. everyone says that small is so much more difficult, but that wasn't the case for me. It had a cover, so evaporation was next to nothing, only had to add water once a month, and never have i seen a more stable system.