Gill issue - Starting of Cottonmouth or Columnaris?

[Cbass]

Hi everyone. Just noticed this AM that one of my tetras gills is inflamed and that there's a small bump on it's mouth. Have a feeling it could be columnaris? No loss of appetite and swims normally. Although one started to isolate itself from the school and really only stays on one side of the tank (I have 11 of them in total). For meds, I have Kanaplex, General Cure and Erythromycin. Water parameters:

pH: 7.6
Ammonia/Nitrites: 0 ppm
Nitrates: 20 ppm
GH/KH: 6/3

Last water change was almost 2 weeks ago (was planning one tomorrow as its my schedule). 
 

[Colu]

I think it would be worth doing a course of kanaplex in food feeding a small amount twice a day for 7 days store any leftover medicated food in the fridge 

Edited June 2, 2022 by Colu

[Cbass]

@Colu Thanks. I was trying to quarantine it, but it's too damn fast and I have too many plants and hardscape. I'm thinking that the only way to administer is to feed the entire school. The problem is that I have is that there are shrimp in the tank and Kanaplex isn't good for invertebrates. 

Edit: Just read that as along as it's not dosed directly in water, it should be ok.......

Edited June 2, 2022 by Cbass

[Colu]

Yes it should be shrimp Safe when added to food 

[Cbass]

Update: No change after a week. I was able to quarantine him and did 1 round of General Cure. Still no change. 

I have a feeling that it could be NTD. The one good thing is that the school can swim around to the left side of the tank. Initially the sick neon would start nipping at the others whenever they got too close. 

May have to euthanize.