I have a 2.5 gallon aquarium that I got as a gift. It has water, sand and a filter, all from an established aquarium. I was keeping a fiddler crab in it but it escaped and plumeted to the floor, later dying a gruesome death. I am too traumatized to get another crab, so what can I put in it? Besides a betta? No bettas. The tank dimensions are 12x6x8 inches. Any ideas are great, not just fish! Thanks a bunch!