I have an established 100 gal. Koi pond with 2 - 1-year-old Koi & 3 small bullfrogs.
The water is clear, the surface has 75%+ of plant coverage, PH is proper, airation is very good, fish are healthy. So why do the Koi hide at the bottom at feeding time until after I leave. Is there something that I can do to coax them to be more sociable? They used to come up to feed in early summer before I got control of the algae problem. Is it possible to train them to come up to eat? Thanks for any ideas.....Kim.

The koi may be shy because they are but a few fish in what for now, seems like a big pond to them. They will eventually outgrow the pond by the time they're a few years old. You may want to start digging a 1000+ gallon pond. Anyway, they could be scared just because they are or because a predator has visited recently. If a raccoon, heron, cat, etc. has been fiddling in the pond, that would scare then. Adding some small fish (goldfish, rosy red minnows, etc.) could act as dither fish which would make the koi feel more at ease to come up. Of course, that would add to the bioload of your small pond. Koi can be taught to eat from your hand. First, feed them normally. Then each day, keep your hand closer and closer to the water and eventually, you can hand feed and touch them. This is easier in a big pond with big koi. Small koi are more skittish which is natural since they should be afraid of more predators.