Cory with wierd spot on mouth

I've had this particular cory for a few months now, when I got him he had a large pink area near his mouth where it looked Iike an infection had occurred. I kept my water very clean by doing 25 percent water changes every other day. The pink soon turned into a white color and the spot got smaller and his mouth looked like it was healing. For the past 3 weeks it has just stayed as a small white/gray area on his mouth but today I noticed a raised lump on it that's white. None of my other corys have anything like this. Im not sure if it's a fungus or something else. My water parameters are 0 ammonia, 0 nitrite, 3 nitrate, and 7.3 PH.

He is still eating and acting normally

I got some better pictures of his mouth

Weird. Never seen that before. @Colin_T might know

That must be damage from the cory trying to digging and hit something hard or maybe columnaris

Edit : I am not the best at corys since I don't keep one myself

When I got him he was in a tank with gravel so I just assumed his mouth was rubbed raw and it was healing but I don't know why it looks like little bumps forming on the patch now. They don't appear to be fuzzy like columnaris or any type of fungus. I'm stumped as to what he has.

presumably a sore that isn't healing.

try doing big daily water changes for a week and then add some salt and see if it helps.

Am I able to add salt with plants and snails in my tank?

You can add rock salt (often sold as aquarium salt), sea salt or swimming pool salt to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

If you only have livebearers (guppies, platies, swordtails, mollies), goldfish or rainbowfish in the tank you can double that dose rate, so you would add 2 heaped tablespoons per 20 litres and if there is no improvement after 48 hours, then increase it so there is a total of 4 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria but the higher dose rate (4 heaped tablespoons per 20 litres) will affect some plants and some snails. The lower dose rate will not affect plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.