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.