I have 8 neon tetras and 3 otos in a 30G, but my parents would like me to add a "bigger" fish. I don't know if it's bc they are getting older and are having trouble seeing the fish (I gave up seeing my otos anyways) but they are very adamant about it. I'll probably add more neon tetras but can anyone offer me some suggestions on what "bigger" fish I can add that won't eat the existing inhabitants? Thank you!