Cory Missing Tail

How strange.
I have a plec in with cories. I've seen the plec chase the cories away from an algae wafer, but the cories haven't sustained any damage. There are also lemon and glass bloodfin tetras in that tank.
Could it be the green fire tetras rather than the plec? They do have a bit of a reputation for nipping fins.

I've always thought that bn plecs were vegetarian, but mine totally hoovers up the frozen food i put in the tank. He's not aggressive but he does use his size to clear the competition for food. I couls easily imagine a cory being accidentally injured if it refused to give way to the plec.

Though I've not heard of a plec sucking on a fishkeeper before. Mine is certainly too timid.

Quick look at this query and one thing stands out to me...  the Cories should have protein tablets or some protein in their diet...  I'd suggest some proper Cory tablets fed at the same time as you pop an algae wafer in the tank for the BN Plec, but in different areas of the tank... 

This is one that I use:  https://www.amazon.co.uk/FishScience-Corydoras-Science-Catfish-Feeders/dp/B075SHGTB1

I had cories for a while in the same tank as tetras (and, briefly, harlequins). They didn't fare well, unfortunately, and seemed to develop missing pieces of tails and fins (among other things). I did catch my two female tetras lurking around immediately behind the cories, clearly waiting for the cories to do their rummaging and avail of whatever they managed to dig up as often a cloud of debris cascaded behind the cories. I'm almost certain the cories' missing tails were caused by the tetras (this species has teeth) although I didn't rule out some being caused by over-amorous mating behaviour among the cories.

Fishes' behaviour does change over time in a tank and it might just be that one of the tankmates or the BN plec has realised, like my tetras did, that they can get a free helping of food from whatever the cories dig up - but in the process have been too eager and taken a mouthful of the cory's tail by accident.

I would suggest:
* increasing the number of cories to at least 6 (and ideally 8-10, if your tank capacity allows); I know our Community Creator says 4 but, generally, the more, the better and it ought to give them more confidence in the presence of the other tankmates (as well as minimise any stress-induced conditions which this might even be);
* doing more and larger water changes to keep the water in optimum condition to let the cory's tail heal (if that doesn't work or the situation deteriorates to the point of finrot, then remove the injured cory and medicate with something like eSHa 2000 or Waterlife Myxazin in a quarantine tank (if you have one plus a spare filter and heater, transferring some filter media across into the QT's spare filter).

Hope that helps.

I tried those Cory sinking pellets too...  They're obviously tasty, coz everybody else in the tank would steal them long before the Cories found them, lol, especially the Amano shrimp...!!!