A while ago, I discovered one my of white cloud minnows (WCMM) was missing his dorsal fin completely. I thought it was odd, but thought it must have been missing since I got him, since you really have to look to see that it's missing.
But the other day I noticed another one is missing his entire dorsal fin, and his other fins were a bit beat up.
So I'm trying to figure out how they're getting injured.
I've got the 10 WCMM, and 1 betta in my 15g.
I've never seen my betta chase them, but that doesn't mean he doesn't. The minnows always steal his food, and they get awfully close to his mouth in the process, though I don't see how an accidental nip could tear off the whole fin...
The filter is a stingray 15. I never noticed a huge suction on the intake, since there's a sponge right in the intake strainer. I've also put a sponge behind the filter, since one of the minnows, and the betta (!) has gotten trapped behind there before. So now nothing can get behind the filter.
There are 3 "boss" minnows. These are 3 of my 5 original minnows. So they're bigger than the newer ones.
Other than that, I've just got the usual things in the tank, heater, thermometer, rocks, a few plants, and sand for substrate.
So what could be injuring the minnows? The betta? Another minnow? The filter?
On the first guy I noticed missing, he's otherwise totally normal, though the fin never grew back. Doesn't affect his swimming at all that I've noticed. Actually, it's kind of funny when he flares at the other minnows, since he doesn't have his dorsal to stick up, the others just ignore him