Yesterday I noticed one of my rosy barbs was missing her upper lip and was very pale. I pulled her out into quarantine and also grabbed another female and another male I think, that looked suspicious to me (1 was pale, not as "shimmery" and vibrant as my other fish, and the other seemed to be a male with very pale colorations, but could go here/there- but he never eats when I feed the tank and sometimes I think he has spots of lesser coloration, so out he goes.) After pulling these 3 fish the one with the missing lip died. Rest of fish (6 tiger barbs, 4 green tiger barbs, 3 remaining rosy barbs and 1 black ruby barb, and a pleco) seem perfectly fine.
BUT my favorite big rosy, I'm not sure if I'm paranoid but it looks like his lips are maybe slightly bigger than normal and showing a lot of white.. but not fluffy... and then sometimes I look at him and he looks fine.
I need to know if I should treat the tank? Does this sound like columnaris? What should I use? I have nerite snails and a common pleco.