i have a guppy that I think has fin rot or maybe something else? There has been no nipping. Water perimeters are .0 ammonia .0 nitrite 10 nitrate. Is this fin rot? I got him at a petsmart so it could be anything. He is the whiteish pinkish one in the photos.
It's hard to see in the photos, its tail shape could be due to a lot of nipping, but it definitely looks wasted away in the second image. I would say fin rot is a likely possibility. Is it rubbing against anything, or acting lethargic?
You could, it depends on the medication though. However the best way to get the meds to actually work is to put the fish in a quarantine tank while you're treating it. I'd recommend aquarium salt, since the infection seems quite mild. Don't use it for too long though, 7 days is the maximum imo. Make sure to do frequent water changes in the quarantine as well.