I’ve had no issues with fish disease for the last couple of years in this tank. Have not introduced any new plants or fish in a long time. But the Priscilla tetras are probably nearing the end of their life, they’ve been around for several years. Today I noticed one spot on one of the tetras (see photo), none of the others have any visible issues. He is alert, going after food at the top of the tank (although I noticed he did spit out a little bit after taking some flakes-unclear). Do you think it’s ich that I need to treat?