Has my Corydoras Hasbrosus got red blotch disease?

Hi everyone, I think I’ve just lost my first Cory to red blotch disease, the other 5 seem fine in the tank. This one hasn’t been swimming much for a couple of days but every time I tried to fish it out it swam away, I’ve just found him on his side. As I caught him he swam away but was all over the place, in the time it took to set up the Hospital tank it looks like it’s succumbed, maybe the added stress was too much.

The question is, do I need to medicate the tank with the others in with anything or just keep an eye on them and keep the water clean?

One of the others has flashed his belly (scratching its side on the sand) once or twice over the last few months but I’m not reading too much into that.

I have a honey Gourami that I treated out of the tank with Epsom salt for constipation, and 2 white skirt terra, the tank is 60l so definitely not overstocked, but three white skirts have all died from odd growths, over the last 4 months (all QT’d before they died).

KH6-10
Nitrate and nitrite 0
GH a bit over 7, much less than 14
pH 7.2
Ammonia is yellow on the seachem indicator (safe)

I’ve followed this up with a 20% water change.

Thanks for any help / advice.

P.S there’s a photo of one of the white skirts too, the lump on the anal fin and also one where the body meets the tail fin

The Corydoras looks like it has a puncture wound.

No idea about the tetras, the picture is blurry and doesn't show the lump well.

Thanks, I wasn’t sure about that with the Cory but not sure what could have done it in the tank! The picture isn’t the best because the fish is so tiny it’s hard to see.

Three of the tetras died with similar lumps but the remaining 2 are doing fine. I know I should have more of them, but long term they aren’t what i want in the tank so I don’t want to just keep buying them for the sake of making a school.