We need to be sure stress or water quality isn't lowering the fishes immune system, opening them up to parasites. Your UV
unit, if working, should be eliminating free swimming parasites, but that's all it can catch.
I suggest some water changes to get the water chemistry on track. If the fish have Ich, then a dip might help, but most of the time they need copper treatment. MV is seen with rapid breathing first as gills are affected. Others on the forum may have additional suggestions, we have all dealt with it.
of 9 is about right. Mine runs from 8-10. You're a bit high. Stop the buffers. Make some water changes.