hey sarah, this is an amazing thread.
iv had a few probs recently. i used to feed 40% oats 40% barley and 20% parakeet mix. but the parakeet mix now has loads of sunflower seeds in it and some mice were getting a bit porky so to speak lol. so i now have them on a hald budgie half parakeet mix that only consists of the tiny round seeds. this seems to be going down much better. they also get mealworms a couple of times a week and small bit mixer is also added into my mix. i am however wanting to completely re-think my mix. i am now useing whole oats ( as they keep the mices teeth down and keep the nutrients in compared to rolled or crushed. ) the only barley i could get was rolled and it was dusty and genrally pants so to speak so i am no longer using that.