This is probably going to sound nuts, but has anyone ever seen a white cloud minnow 'guard' a spot in the tank? I have one longfin that seems to have taken up residence in front of my hillstream loach's cave. It kind of swims in place, and either chases away any others, or flares at them for the bit before going back to the spot. It acts normal if I walk past, or if it's feeding time.
It looks completely fine, it's just that swimming in place just above the gravel is kinda weird.