I was doing a fish in cycle with 4 bandit/melini Cory catfish in a 10 gallon. I know not a good idea to do a fish-in cycle but i'm a beginner. 3 of them died during the cycle but 1 survived when it was all over. It was doing great for the next 2 weeks after the cycle, it just looked bored so I got him 3 friends of the same kind. Plus 4 ghost shrimp and 2 moss balls. The first day was great, he was finally acting like a Cory again. This morning though he was laying on his side not moving and when I tried to pick him up with the net (thinking he was dead) he started to swim uncontrollably, left, right, circles, upside down, and sideways. This isn't a first for me because that is what happened to the last 3. My question is why is he acting like this, why is he going to die after he was fine the day before. The water parameters are good. Was adding 3 fish and 4 ghost shrimp to much stress for him or what? Also I thought that maybe the nitrogen cycle put him under so much stress that his immune system was weak and when the new fish came in it gave him something but that does not sound right since the last 3 fish had the same thing. 
