Injured goldfish!

Three days ago, I found that one of my goldfish has a good portion of her scales gone. I think she scratched herself on some of the tank decor. I've been doing 50% daily water changes to keep the water clean. No medicine or chemicals used so far, but I noticed that the "wound" is turning black. Not sure if it's from rubbing the decors (I have some lava rock), or if it's rotting. Other than that, she's swimming and eating well. It doesn't seem to bother her at all.

The tankmates (another oranda and a common pleco) seems ok, and they're not taking advantage of the injured one.
I don't have a hospital tank at the moment.. Should I get one? Should I get some medicine, too?

Here are some photos of the injury

Melafix would be good for something like this. The black is actually signs of healing.

Deanasue said:

Melafix would be good for something like this. The black is actually signs of healing.

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Whew! that's good. I'm getting the Melafix today. thanks!!

Add 2 heaped tablespoons of rock salt for every 20 litres (5 gallons) of tank water. Keep the salt in there for at least 2 weeks but not more than 4 weeks.

If you do water changes while using salt, add salt to the new water before adding it to the tank so the salinity (salt level) in the tank remains stable.

Colin_T said:

Add 2 heaped tablespoons of rock salt for every 20 litres (5 gallons) of tank water. Keep the salt in there for at least 2 weeks but not more than 4 weeks.

If you do water changes while using salt, add salt to the new water before adding it to the tank so the salinity (salt level) in the tank remains stable.

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The wound looks clean now. It looks like new, very light-colored scales are already replacing the old ones. Should I still follow up with the salt treatment, just to be sure?

salt won't hurt and will help to reduce the chance of any infections