Salt in Pond to treat disease

Hi

I have a couple of fish with ulcers , also white fungusy stuff growing
on them, i used Melafix

After using Melafix the goldfish started to get what can be best
described as black / blue / dark red colour around the fungus areas..
I will get a picture if i can, It looks pretty Ugly , it almost looks
like brusing?? The fish seems ok ish it isnt too lazy it comes up with
the other for food although i havent caught it eating yet

I read somewhere that Salt was a goood all round treatment.

My Pond is just 1000L big , how much Salt do i need to add. If
possible Teaspoon / Tablespoons would help as i dont have a good set
of scales

W