I've had 6 neon tetras in my 10-gallon tank for almost a year now. A few months ago two died from Neon Tetra Disease, and they seem to have been jumpier and schooling together a lot more often than before. I've heard that I have to have at least 6 in a 10-gallon tank, so should I get more? I also have about ten cherry shrimp in the tank. Could I possibly group them together with some golden neon tetras/some other fish, or should I just stick to the ones I have now? Will there be any problems (such as aggression) if I put new fish in there?