I plan to give this second dose its time to work then do a large change again, then give the tank the final dose to finish out the treatment. So Tuesday Ill clean out the tank again. I have been watching the water stats and aside from having hard water due to the water in my state. All of the stats have been well in optimum conditions. As I said the infection has either reduced or ruptured and is flowing out. Hopefully the Kanamycin is helping clear the infection up.It does not look like a physical injury. Even if it began as one (probably not) is is now an open ulcer with an additional secondary infection. Weekly water changes (>50%) are needed regularly. Those are better than an ocasional 90% water change. Should be reversible if conditions are improved. Good luck!