I've toyed with the idea of using loose minerals for awhile now. What's been holding me back is I'm not really sure where to start. What minerals should I use? How do I store them? How much do I provide? Is it based on weight? What changes when I have to supply both horses with them in the same pasture/shelters and from the same "holders"? Where can I buy the minerals? Is there something I should specifically avoid? I'm located in the Pacific Northwest, and to be more specific, near Seattle, Washington.