There are a few good videos on this on You Tube. http://youtu.be/RQw_tgdCwlY
I started looking at this not only that I like bigger koi, but I wanted healthier koi. One thing he talkes about is the gradual transition from feeding cold supplement wheat germ to the high protein diet. I have a zip lock bag that I will make my combination of food. Even in the summer months, he suggests a small percentage of the food to be wheat germ. It's just easier on the koi's stomach.
Now with the colder months coming, I'm starting to ween them off the high protein. I've found the results are great. The koi look healthy, they're active, and I've noticed a big growth difference from last year. Currently I use a standard cold supplement wheat germ, a high protein mix, and a silk worm protein mix. Again, this may sound like allot, but the bags of food last forever.

Hope this helps

Craig

So you purchase it in bulk and create your own mix?

I'm watching this now and the guy is hilarious lol

Wow...everyone should watch these videos - they are awesome!!!

i feed my fish rise fish food at 30$ for a 50lb bag.been using it for over 12 yrs. my fish are healthy and huge.

I thought that was a great series also. Makes me wish I he was on the East coast. I will just buy a single bag. I'm not promoting any brands. I know you can spend allot of money on high quality koi food.
What I use, Aquascapes cold water pellet (high wheat germ) & color enhancing, with Hikari's silkworm selects. The silkworm pellets are a little bigger. As the fish grow you may want to switch to stick formulas.

I hope this helps!