black neon tetra swims vertically???

[electricaleng]

Hi, i'm new to the forums. i have a 5 gal hex by marineland (eclipse-like filter-hood) I have 3 black neon tetras in it and one of them has been swimming around almost vertically for the past few days. The flow thru the tank is such that the fish all orient themselves facing the left and can kind of casually swim against the current without moving a whole lot unless they want to. I thought initially this may be why, but the other 2 fish don't behave like this. I'm concerned that this one may be sick.

Is anyone familiar with this kind of behavior?

 

[WILDER]

Can you post water stats in ammonia,nitrite,nitrate,and ph, what do you feed the fish, does the fish look abit bloated, try some shelled peas and daphnia to give the fish a flush through to see if that helps, that tank isn't big enough for shoaling fish, and you shouldn't really be keeping the black neons as they need to be in a group no less than six.