Koi feeding needs to be done carefully and in moderation. Koi are not able to digest large amounts of food at once and overfeeding can contaminate the water in a pond. It's best to feed small quantities at several intervals. I like to feed them just a few pellets at a time and watch them eat it all before giving them more. When they slow down I know they are getting full. This doesn't take as much time as you think if you buy koi food pellets to the appropriate size for the fish your feeding.

1-2" Koi = 0.06" pellets

2-6' Koi + 0.25" Pellets

12" + Koi = 0.3" pellets

Feeding in this manner as well as feeding in the same location all the time helps to tame them into friendly little pets you can actually touch and even pet. When I build a Koi pond I always make a huge flat and stable stone just above the surface of the water. I overhang the stone (Usually an artificial rock) over a deep hole where the large fish can swim right up to and even underneath while They eat. I call this a "Feeding Stone". It also helps the fish to quickly tame as they feel safe in the deep water with a nearby ledge to hideout under.