Sinking Lionhead

Hi all - I have a Lionhead that seems to have no bouyancy. It can swim fine
and will eat at least some food when feeding, but since it cant float it
does little foraging which requires the ol headstand. Water parameters are
fine (except nitrates are 60ish) and there are no obviously external
symptoms. VERY infrequently ( I might observe this once a day) it will dart
to the top for a gulp of air and then settle right back on the bottom,
blowing air bubles on the way. It is definitely loosing weight and is
getting skinnier, not blown up. I am guessing this may be a swimbladder
problem so I have begun feeding it and it's tank mates medicated food.
Beyond that I am at a loss for anything to even try. Any suggestions would
be appreciated!
Bill Brister - Austin, Texas