Hi. We have one black moor in a 10 gal tank. The past few weeks he floats vertically, next to the filter and moving only one fin. He stays there unless we are next to the aquarium. He seems to swim fine when we are near the aquarium but the moment we leave, he is back in the corner in the vertical position. Is he dying? He does eat. Before he started this weird behavior, he was swimming on his back and seemed to have problems turning himself right side up to swim normally. We thought he was dying then but appears to be okay. Water temperatures is okay, tank is clean, filters fine etc. Any information will be most be appreciated. Thanks.