I saw it this morning and started researching because I am dealing with an ich outbreak due to recent overcrowding. It hasn't changed or gotten worse but I don't know if it's infected or a disease. If you can't see my koi has an orange yellow colored scale that looks like it's been pulled away from his body there is no blood, I recently received a decorative pirate ship and it's the only thing that could have hurt him. I want to ask would it harm him if I did try to treat the ich or will the medicine help if so is there a specific brand I should use? I have two small gold fish and one koi about 3 inches long In a ten gallon tank it used to only be five but my last fish was a surprise and I usually have it at 75-80 degrees.
First of all your tank is way too small. The minimum tank for one baby koi is 100 liters and this is for the first year you have it. Goldfish need about the same amount of water for one fish but they grow slower. If you start with a 100 liter tank for one fish you add 50 liters for each new fish (this is for both koi and goldfish).
When you get the medication against ich try to get one that is only treating ich or you will get problems if it kills the good bacteria in your tank and filter.
If the koi have a wound you need to add some aquarium salt and the dosage to use is 0,3% this is a safe concentration for long time use. The salt will neutralize the effect of nitrite in the water and stimulate the healing of your fish by increasing the blood flow in the skin of your fish.
For now I think the only thing you need to do is to keep an eye on the injury on your koi. If you see it getting red or it becomes infected by fungi you need to start treating it.
The common treatment for small injuries in the skin of koi is potassium permanganate dissolved in water you can buy this in any pharmacy. It is a liquid and you apply this by a q-tip directly on the wound of your fish twice a day for a week. And try not to spill any it makes everything purple.
Remember not to buy the powder but the premixed low concentration potassium permanganate the type used to treat wounds on pets and people and now fish.
Try to keep the temperature around 25C=77F it is best to cut back on feeding for the time you treat against the ich.
Fish in the carp family are seen as dirty, they produce a lot of waste so you need good filtration of the water.
And please get a larger tank for your fish.