Sick Julii Cory

I cleaned my tank yesterday and did a 25% water change, I noticed last night my Cory had a red blotch on its side and when goggling it suggested to do a salt bath for 15mins and return the Cory back to the tank , done this and this morning the red blotch has gone however still one very unhappy Cory sitting at the bottom clamped fins and hasn’t eaten today , upon looking further in the day he seems to have a graze in the same spot but it also looks white ? It’s not just a white looking spotting like ich it looks like a graze , still hasn’t moved much from same position since morning and breathing heavy , I’ve checked parameters but only with a dip stick as that’s all I have atm and they all read good any help or advice what could be wrong with him

Cories do not respond well to salt baths, it's looking now like he's having some excessive slime coat issues. It very well could be a bacterial problem, gravel isn't ideal substrate for them. It hosts a lot of waste inside the cracks and is more likely to cause infection to the bottom dwelling fish.

I would suggest swapping over to sand instead of gravel

I avoid any bath at nearly all cost... Salt bath... Loll.

The only time I had to give a "bath" to a fish, was in case of "chronical" external parasites infection.

And it was not salt. It was methylene blue, malachite green and a ich medicine I prefer. Not for 10 minutes but 24 hours. Not a single one I know will let off in 10 minutes with salt.

From the pictures it looks like it is skinny, the belly doesn't seem right. that could suggest internal organ problems or parasites. If all the other fish are going well and there has no late un-quarantined additions.

I would think that this fish is suffering a digestive organ failure. The cluttered scales on the belly lets think of that, or an internal parasite.

So any advice what my next steps should be please ?

Check in the next weeks if it's an illness or a singular condition. Watch closely other fishes for any similar symptoms.

"Shrunken bellies" on top of all.

Remove affected fishes before they die.

Introduce sand. Start with an easy place, remove a good layer of your pebbles and cover it with wet smooth sand. don't pour it dry...

Cover a part of the bottom and look how it goes... I mean CassCats is right. Your cories shows pretty bad barbel erosion.

This also could mean that they are forced to forage a lot more than required. I had hundreds of cories having no problem with similar substrate as yours, but the fish where fed, filled to the top and where not foraging.

They where taking sun baths.

I'd opt to deworm them, as I agree with MaloK here with the sunken belly, I'd choose flubendazole and dose that to the water, or use fenbendozole or levamisole in food (these last 2 are not water soluble so they cannot be dosed to water and work well.

Switch the substrate to sand and do a good water change to ensure the bacteria levels are lowered.