That is exactly what is going on. If you grow up loving and eating McDonalds and someone all of a sudden served you a Veggie burger, would you really want it over a good old fashion BigMac. Same thing happens with fish food. So if your going to uuse good food, try good food treats. Orange pulp, lemon pulp, water melon, dew melon, cantaloupe ( all with seeds removed) Krill, silk worms, etc are great treats that can help give koi vitamins, are great for the digestive tract, and are extremely healthy for your Koi, and they like it too, As for Kenzen, I recommend feeding it for one season. the first month they are still adapting to it. By the second month you should start seeing better muscle tone, increased growth rate, clearer water and better water quality overall. By month three and four skin color should start showing more improvement, and by this point they are used to the food and will be eagerly accepting it. My biggest problem with Kenzen, It's to darn high to feed to 100 Koi.