I brought home a pair of Denison barbs from my LFS last weekend and put them into my community 38G tank. At first they both seemed ok, going through the usual hiding and exploring of the tank while they acclimitized. Then a few days later one of the barbs starts swimming parallel with the back glass, so it was swimming sideways. The back glass is painted black so it messing with it? Or does it have a swim bladder problem? Thing is though that when I turn on the lights in the morning it seems to swim around fine and upright for a while then eventually it swims up to the back top corner and start swimming sideways against the glass again. 
