one of the nicest looking tanks i have seen was a 15 gallon with tiny pipefish, a couple chuunks of live rock, some star polyps, red and purple mushrooms, 5 porcelain crabs, a couple shrimp that i dont know the species and some scarlet hermits. the color contrast was amazing, and in that small a tank you didnt have to LOOK for stuff, it was all in plain view, alot of activity with what i was told was very little upkeep. low bioload, low runing cost. seemed like the perfect tank for the size.