I have five rummynose at the moment. Previously four out of a batch of eight, four died the first two days when introduced into the tank. The only social Rummynose is the newest one, the others hang out in the back corner of the tank avoiding all the action by the other fish. I don't know what to do. When I change the water they shoal around but don't school, that is about as much action that goes on. Now I am hesitant to add more because I run the risk of overstocking the 20 gallons as well as the risk of ending up with a bunch of antisocial fish that don't even bother schooling around the tank. Any ideas?