Hey Kent -
Good advice. I too have noticed that koi will eat the roots of floating plants. One thing that has always boggled me is that the fish in my pond do NOT eat my hyacinth and lettuce. I have mostly koi with some that are around the 14 inch mark. I usually feed them well, but sometimes I get caught on a job for about 4 days at a time and done get a chance to feed them. They seem to find plenty of food and pluck at the small amounts of hair algae.
However, I was just at another customers pond and her koi mow the roots off of her floating plants daily and she feeds her fish more often than I do. She likes to have some hyacinth in the filter (where the fish can't get at them) and some in a floating ring in the pond. Over time she switches them back and forth so that they can re-grow and it seems to work pretty well.
For me, the question is still out as to why some koi eat the roots of plants, while some in other ponds do not.
Maybe someday we will figure it out!
Thanks again,