In a few of my tanks, I have noticed my cories, and a few bristlenose plecos, flashing against caves, driftwood, etc. I do not see any signs of parasites on them, and am not eager to dose with medicine since most of my tanks have scaleless fish and inverts. I had an anchor worm scare in my 90 a few months ago, but saw only one worm, and medicated the tanks. No sign of ich, velvet, anything else. What else could be causing this?
