My chicks are 9 weeks old. They are still eating a mix of chick feed. It is a bucket of 18%medicated and 20%unmedicated feed. The hatchery I bought them from recommends switching to a 15% unmedicated pullet grower. I really don't want to waste the feed I have which may last another 2 weeks. Is it ok to use it until it runs out or should I switch?