A lone fish

[Cypilk]

I think I have an unhealthy fish. In my 25 gallon tank, I have 7 Zebra Danios and 3 Neon Tetras. One of the 7 Danios are baby-sized compared to the other 6. I would say he is about 2.5 cm long. Just recently after I did another routine water change, I noticed the small Danio off to the corner to himself and not schooling with the other 6 fish. I know that they get a little nippy, and he is uaually the one that always gets picked on, but it didn't stop him from schooling with the other fish. What should I do?

[dskidmore]

Good observation, catching a problem when it's just behavioral. It's a bit hard to say at this point what might be wrong though. Keep a close eye on him, and consider getting a QT set up in case he's sick.