Yesterday I did a 20% water change and added AlgaeFix to my pond. Koi started skimming and hovering at the surface and looked oily. I immediately did another water change, while keeping the aerator on, they seemed to do a little better. I also sprayed water hose in the air letting water drop on the ponds surface and added a few dechlorination salts. They seemed to do much better. This might have been wishful thinking. This morning I looked out at the pond and saw what I thought was one koi floating at the top. I went out and it was. My favorite one. The biggest one. The leader. The one who ate from my hand and taught the others that I was safe and it was okay to eat from my hand. I am devastated.