Mysterious Cory Injuries

[MrsHyde1018]

I have about 9 Cory in a 30 gallon tank with 5 assorted Guppy females and their fry. (2 pepper, 3 green, 4 Julie (maze print) corys to be exact.)

In the last month that I’ve been watching the Cory (they’ve been in this tank for about 2-3 months) one green has lost the bottom half of his mouth, one Julie has had its sucker mouth picked completely off while a couple other Julie’s and some of the green’s are missing their whiskers. The Peppers remain unharmed but are the largest of the group, which led my husband to suspect they might be the culprits. But cory’s are so gentle, I can’t see them tearing into each other like this.
the only other fish in the tank are my guppies, which I couldnt see them doing this either. But what else could it be??

i had an albino cory (separate tank) that had the same damages done to it as now; picked at until his mouth was gone by what I thought were either black kuhli loaches or our clown pleco in a 20 gallon we still have to this day, but now that it’s happening again I’m stumped. Any ideas or advice?

 

[DoubleDutch]

Peppereds didn't do this. Possible a bacterial issue. What substrate do they have.

 

[Retired Viking]

I use sand, less chance of injury to my cory catfish.

 

[MrsHyde1018]

Peppereds didn't do this. Possible a bacterial issue. What substrate do they have.

I use volcanic soil, for our live plants. I don’t *understand how this would be a bacteria issue, could you explain?

 

[Byron]

I use volcanic soil, for our live plants. I don’t *understand how this would be a bacteria issue, could you explain?

This is the issue...rough volcanic soil. Cories should only be housed over very soft sand; aquarium river sand is best, but some brands of play sand are also OK. It is most likely the sharpness but in such a substrate bacteria can cause trouble for substrate fish. There are many species of bacteria besides the often-thought-of nitrifying species, and these live primarily in the substrate where they break down the organic matter.

Many years ago (before I understood the issue or recognized it) I had Flourite plant substrate in one tank, and the cories within a matter of days developed basically identical symptoms. Fortunately I got them out quickly, and over sand, and happily all recovered.

 

[itiwhetu]

I would be checking your Nitrate levels in your tank. Make sure you do regular water changes and keep the substrate as clean as possible. Cory's don't like any sharp objects so the substrate they are on needs to be smooth and rounded