@NCaquatics I'm starting to wonder whether I agree with you about neons... do you know whether cardinals can be the same way? I added three male guppies to the 55 gallon community tank once, and all of them wound up with splits in their tails. Water was fine, and I hadn't thought it could have been another fish in there. The two loaches, maybe, but they they tend to keep to themselves at the bottom while the guppies stayed at the top. Mollies and platies were okay, couldn't see any other fin problems, except the guppies tails. Moved them back to another tank and the tails healed up fine.
There are six neons and six cardinals in there. I haven't seen them act aggressively, but perhaps they were the culprits?