I stocked my tank a few weeks ago with a large number of juvenile fish. Right from the start I had one fish that seemed to hide in the bottom corner of the tank. It looks relatively healthy, but it is still acting the same 3 weeks later and I don't see it eating anything at feeding time. Yesterday it was acting particularly lethargic. Swimming in a nearly upright position in the bottom corner. Should I relocate the fish to another tank or take some other sort of measures? Thoughts?