Swollen back end on my Dojo

[loachioto]

Hi all,

I was wondering if anyone could help me with one of my Dojo loaches.

Basically, a couple of weeks ago, the back end started to swell up. It also has what looks like some blisters forming. I have 3 other loaches in there which seem fine, and behaviourally, I don't see any change. He is still active, eats food, etc.

I usually do a water change a couple of times a week (30-40% or so)

I have attached some pictures. Any advice would be appreciated.

https://imgur.com/a/uvDsQbR