Is this fin rot?

[Rosiebb]

I brought home four “hifin tetras” two weeks ago to school with my other two black skirt tetras. When I first added them I noticed their fins didn’t look too good but they’ve started to look better so I assume it’s just from the conditions of the pet store tank. One of them however developed a split in its tail fin last week and a couple days ago I noticed the dark spot on the edge of the split. Does it look like fin rot or is this something else? I’ve never dealt with this before and I tried asking on Reddit but didn’t receive any replies. I clean the tank every two weeks which includes a water change and gravel cleaning. I have hikari micro pellets and dried blood worms to feed them. I also have three oto catfish that eat hikari mini algae wafers and cucumber. I know sometimes fish can injure themselves on sharp edges and I do have a section of rough rocks but haven’t had any issues before with my other fish. Any advice or recommendations are greatly appreciated!!!

 

[Andy Sager]

I brought home four “hifin tetras” two weeks ago to school with my other two black skirt tetras. When I first added them I noticed their fins didn’t look too good but they’ve started to look better so I assume it’s just from the conditions of the pet store tank. One of them however developed a split in its tail fin last week and a couple days ago I noticed the dark spot on the edge of the split. Does it look like fin rot or is this something else? I’ve never dealt with this before and I tried asking on Reddit but didn’t receive any replies. I clean the tank every two weeks which includes a water change and gravel cleaning. I have hikari micro pellets and dried blood worms to feed them. I also have three oto catfish that eat hikari mini algae wafers and cucumber. I know sometimes fish can injure themselves on sharp edges and I do have a section of rough rocks but haven’t had any issues before with my other fish. Any advice or recommendations are greatly appreciated!!!

Black skirt Tetras can be a bit nippy with others in their school so I would not jump to a fin rot conclusion. If the tear gets worse or you see bloody edges, then you have something to be concerned about.
I would take some time and watch the tank from a distance so that you can see how the fish interact with each other without you as a distraction. If you see them nipping each other, you probably have multiple males that are trying to show their superiority in the school. At that point, you will have to decide if you want to remove the offender or remove the weaker males or let them figure it out for themselves and just watch for too much fin damage.