you might over fed them . what ever they are not eating , you have to remove it or else you will have ammonia problem and the koi start to get sick.

www.koi-town.com

Hi Sophsmom, for beginners a good rule of thumb is feed your koi as much as they can eat in a 4 to 5 minute period It is best to feed them 2 to 3 times a day. If you feed them to much just once a day they can develop a bloated stomach. Koi-town is correct, all that uneaten food will turn into ammonia in your pond.

I hope this helps....
Craig