I keep mine with sterbai cories so I don't see how tetras would be a problem. They chase everyone away from their shells but they're not aggressive. In a 20 long you could possibly do 3 pairs. Mine dig the sand up all the time and I replant things weekly. Not a big deal just annoying. Mine love flake food and the tank is at 78. They just bred for me the first time since I've had them. I pulled the fry and have 7 little swimmers in the breeder box. Just make sure you have lots of shells. My pair has gone through three shells before deciding on the shell they spawned in. They have great personalities. Super fun fish. They stare back at me through the glass.