Had 2 of my koi get nipped by a heron. Not really deep wounds. More of a pretty good scratch just to the right of the top of the back not touching the gills. They are still swimming normally about 4 days after it happened. I fed a few multi season pellets to test and they both came to me and ate from my hand. I have covered the pond with a tarp a couple of feet above the water. Right now catching them is not an option. What is the best treatment I can add directly to pond to help them heal? Thanks.