Most on this board will change water if nitrAtes get over 20ppm. NitrAtes are not really toxic untill they get into the 100+ppm range.
Maybe your pictus injured his barbel?
good luck
things in a fish tank like rocks and such can damage any catfish barbel very easily since they are so sensitive and light. Maybe it could be rubbing hard objects such as sharp rocks or something in your tank?
