I have a 55 gallon with 15 2-3" Demasoni and 6 3" Cherry Red Zebras. They've all been in the tank about 2 months. Recently, I've noticed a handful of the Dems have nipped fins. I know that they're generally buttheads, but should this be a red flag or is it par for the course with Dems? I don't want to miss an early warning sign and have the aggression escalate, but if this is just how they are, I'll deal with it. When I watch the Demasoni, I don't have anybody hiding excessively and everybody comes running at feeding times. There's plenty of chasing, but I've never witnessed a big fight. I suspect that I have two holding female Dems and a holding red zebra as well. Advice?