I agree with Margaid, it is the ratios of the specific grains to look out for, and also the age, breed of the bird, consider whether they are laying hens etc....
Red peanut skins would be a good addition, I am not sure however, how much to add this would depend on how much protein they would contribute. You would want to get the overall protein content to around 14 - 15% as a general rule, again this need could be lower depending on the quality of free-range and or growth/moulting factors where the protein depend will be higher, although very slightly.