I have a 10g nano with a wheelers goby and tiger pistol shrimp. 2 hermits and a snail. Going to get another small fish probably a firefish in about two weeks. Two is the most even if you keep your water clean there's just not enough space. Especially with all the rock in the way. It's great for pistols and gobies- they are really cool and if they aren't scared off by other fish you see them all the time. A lot of people don't have much success with these because they have large tanks and lose sight of them. My 10g is perfect for what I have. My goby eats out of my hand and my pistol is starting to get really close to ne when feeding.