Ugly tubing to ugly up your pond and hide the colorful fish when they surface to feed? Bite the bullet and net the uneaten floating food as a part of the enjoyment of Koi keeping. Pond fish are like grazing animals. Grazing animals are not like humans who bolt down a 4 course dinner in 15 seconds and expect all other species to do the same. The bigger the fish, the longer time they need to eat, so wait 30 minutes before netting the uneaten food and watch them as they play with each other and their as a part of their dining experience. Or feed your pond fish live food. Every other day feed 100% protein, their 'natural' live food that will sink to the bottom. The fish will soon spot you coming when you have a dozen or so earthworms and they will come up and grab them out of your hand. No worries. In the Spring, Summer, and Fall, if you throw a handful of rinsed live earthworms every other day into your pond, not one worm will die of drowning to be found rotting in your skimmers. If you are thinking "ugh, slimy worms for slimy fish" you need another hobby. Bait stores have live earthworms. Doctors Foster and Smith have floating fish foods. Between the two excellent sources your pond fish will enjoy excellent health which is what you want, right?