I've had a few of my cardinals recently develop what look like bubbles or blisters at the base of fins with a tiny white bit inside. I've been treating with paraguard for a week now. The fish that originally had the issue seems fine but another has now popped up. I'll probably keep with that since the first guy recovered, but I'd still like to know what it is.
Ammonia and nitrites are now 0 and have been for 5 days or so (not the case at the onset). Nitrate is 20-40ppm due to easy green.
It is hard to get a clear picture but you can mostly see it by the anal fin.