Friday we started the switch to Fromm puppy. We started with 3/4 to 1/4 for a few days. I ended up having quite a bit of the old food (Nutro), and I don't want to waste it, so is it okay to mix 1/2 and 1/2 and for the switch to go on a long time? Like 2-3 weeks? She is having no problems so far, and seems to like it.