Oscar acting weird

I have 2 oscars in a 125g, both about 9 inches long. the tiger oscar
has been acting strangly. hanging out by himself behind a rock wall i
made, rarely coming to the top for food. sometimes hangs out in the
plants vertically with his head faceing down. seems very lathargic.
he recently cut himself on a rock a week ago, but has been healing. I
see no signs of HITH or anything else. I did a water change, clean out
the tank, filters, added some salt, raised the temp. Any other
suggestions?