I've had two FBTs in a ten gallon tank for the past year. This past weekend I upgraded to a 20 gallon to give them more space. The female FBT had a difficult adjustment at first but has calmed down and seems to be fine. The male on the other hand seems sluggish, and is not eating much. I moved them out of the ten gallon setup because the tank had begun to stink and gotten to be difficult to keep clean. Here is a picture of the male. Please let me know by its appearance whether or not it is in need of seeing a veterinarian.