75 Gallon Tank Worried my corydoras is sick, grey stuff on mouth

75 gallon,HOB filter, with 22 corydoras, ammonia at 0, nitrite at 0, Nitrate at 0. One of my albino Cory's has something gray on it mouth. I have not noticed it before, but I am not sure when it appeared or if she always had it. We are about to leave out of town and I am panicking that she is sick with something. Has anyone seen this before ( in pic). She is swimming around normally and eating. Any help would be appreciated.

 

What is it fed ?

 

What is it fed ?

Primarily northfin community sinking pellets. Once in a while they get frozen blood worms, emerald entree, brine shrimp, or algae wafers. I did give them the algae wafers a couple of days ago.

 

I'd skip the algaewafers (they hardly get nutrition from these : they aren't algae-eaters) and feed more carnivorious food.

I asked because it looks like a lack of certain protein / minerals / vitamins.
The Nothfin stuff doesn't look too bad though.

 

Ok, I will do more meaty foods. They go nuts for the algae wafers that is why I give them to them and only about once or twice a month. Thank you so much for the help.

 

Try some shrimppellets