We hear this quetsion at least once a year. It's not a bad thing, and we have the answer.
You have found The Koi Food Shack on the interwebs, noticed the great value offered, and decided to try out a new feed for your pond fish. Every one of our buyers have been there at some point.
You take delivery of your first order, and anxiously run to the pond with a scoop of new KFS food. You toss in the food and await the happy reaction of your pond beauties. A minute, or two or three go by, and you notice the fish are not eating! OH NO...what's wrong??? Bad thoughts begin to go through your mind. DON'T WORRY!!! 99% of the time, there is a missed step involved.
You forgot to slowly introduce the NEW food alongside the previous feed the fish are accustomed to eating! It is a simple error, and very easlly corrected.
The best way to begin "training" your fish to eat their new diet, is to introduce small amounts at a time. Give your fish 6 of the old pellets and 6 of the new pellets to begin with. They will likely eat the pellets they are used to eating first, seemingly snubbing their noses at the new feed you have just graciously purchased for them. Nothing to worry about. Sit back, and continue to watch. They are hungry, and they will become curious about the remaining pellets that are floating above them, and within a few minutes, will either start sampling the new feed, or they'll just eat it without pause. Once they see that it is just as tasty, and even more so than the old type of food, they will be ready for you to introduce more of the new pellets. This time, don't give them ANY of the older food at all. Give them 12 of the new pellets, and wait for them to eat them all. Do not give them any more until they eat it all. If for some reason, they are still being bullish about the new pellets, clean the remaining pellets from the pond, and walk away for 15 minutes. Then come back and introduce 6 more of the new pellets to them and wait until they eat them all before giving them more. Don't shovel a whole bunch of pellets in at once until you are sure they are going to devour the food in it's entirety in one feeding.
Time and time again, this method works very well. Your fish develop habits over time just like we do. Give them an opportunity to become acclamated to the new feed, they will come around, and you will be a happy pondmaster!