Me too. Flukes infestation appears to be somewhat easy to solve (at least bring down to controllable levels). Bacteria infection. I don't know... I've never needed to treat my fish like this before. Taken care of everything from Goldies, discus to reef tank for decades... nothing is as difficult as imported japanese koi. LOL! Maybe just a bad start for me.
Let me add another story. I left my net pond net (22" - no handle on it) on ledge of the pond. I moved it to another spot on the pond and walked away for 1 minute. It fell into the pond and I heard a big splash (not the net but from a fish). Next thing I knew, scales floating around in water (probably lost 4-5). 2nd Kohaku got nice dent on back of head just behind gill plate (4th pic from left of signature pic). Doh! That was 3 days ago. No infection yet. Crossing my fingers. That guy appears to be in perfect health, besides missing scales and dent. Bowled it for inspection and mine as well rub it down with some debride ointment. I was so angry at myself but I cooled off.