Hi dreamer, The cloves can be used at 5 drops per gallon and you will get different results depending on eugenol dose, pH and temperature.
Topically treating the ulcer is easy but specific. You want to dry it, remove dead tissue and wipe it with a cotton ball soaked in betadine. This is a mild burning material. You will rub the ulcer to bring out SLIGHT bleeding or at least fresh skin. After that ADD NOTHING ELSE other than a waterproof ointment with antibiotic and steroid. This will take out the swelling and kill local bacteria. Most newbies are completely confused by the mountains of information out there regarding treatment and as a result burn new healing tissue over and over, causing more infection. Do not use TWO topical antiseptics as they burn too much healthy tissue. And do not use the betadine more than one or two times. Once you see white tissue appearing stop! Just add the antibiotic ointment. You can get the antibiotic at your dentist ( used for gum disease) or at the Vets( used for dogs eyes). This must be used in conjunction with injectables that attack the ulcer from the inside out as I mentioned. It is a two prong approach.
Judy mentioned that her koi had ulcers but no scars. Sounds like someone has over run their own headlights!

Depending on the stage of the ulcer, all ulcers leave scars! Can’t be helped! At best, the below the lateral line ucler will disappear in the white ground. But once a scale is lost from a pitted ulcer- it is usually gone for good or grows back but is always ‘telling’. This is because the infection effects the base cells that generated the scale that was lost. You can clean out the scale pockets and that can save a scale. But an ulcer leaves a scar. The only issue then is how advanced the ulcer is.