Okay, so we have year old hens. They've been on layer rations since last fall or so. We also have pullets. So far, I've been able to keep them eating different foods, but now they are all mixed in the run AND we will eventually be adding our banty ducks which are only 2.5 weeks old right now. The brand of feed I use is good for chickens and ducks (I don't know if this is common or not) but they are different ages. How the heck do I keep everyone eating the right feed? I'm sure you folks have figured this out, yes???
When I integrated my 13 week old pullets with my older girls, I just put them all on an all-purpose feed (Purine flock raiser, I believe). The laying hens seemed to be getting enough calcium from oyster shell, etc, without the layer feed. I'm not sure what to tell you about the ducks, though. I'm sure someone who has mixed all three will come along soon! If worse comes to worse, you may have to make a sort of 'creep-feeder' small enough to only allow the ducks to get in and eat the food.