Ghost Catfish Missing Fin

[charmscale]

My ghost catfish is missing part of its tail. It's swimming in circles or not at all. I've moved it into my quarantine tank, which is doubling as housing for a betta. Is it okay in with the betta? Also, what could have caused this missing fin? I have four more in my tank right now, in with whatever is the culprit. The suspects are six dojo loaches, six neon tetras, and six hatchetfish, as well as the other glass catfish. Which of them did it, or could it be some sort of disease? Also, what do I do with the injured glass catfish now, if it lasts the night. It doesn't look good. 
I do water changes whenever the nitrates get high enough, about once a month. There is no ammonia or nitrites, and very little nitrates, but the water is very hard. The pH is 7.

 

[THATcichlidGUY]

Well for starts you should be doing water changes weekly, other things build up in the water column than just nitrates that are harmful in high concentrations. Fresh clean water is key as its brings minerals into the aquarium that get depleted, also might want to add a little salt to what ever aquarium he's as it helps in fin regrowth. Keep the light off so his stress level is low and cross your fingers.

 

[ncguppy830]

another thing how big are the tanks?

 

[charmscale]

60 gallon. 

He died, by the way.

Any idea what happened to his fin? 

 

[ncguppy830]

tough, sometimes the weakest of the school gets picked on, maybe thats why.