Sweet feed is not really an economical choice nor a really great feed. You are paying a lot for corn, grain by-products and sugar. Pelleted feeds are not much better and you are paying a lot for grain by-products and incomplete cheap mineral. You are onto the right track with soaking alfalfa pellets, but a better choice is hay chaff. Many stores now carry bagged chaff so you don't have to cut your own like I do. A simple and easy mix is to take crimped oats, mix it with chaff, wet and feed. Growing foals need quality protein, fiber, fat and vitamins. Buying a good vitamin supplement is essential to proper growth. Foals actually need fat for proper joint development. I've seen just as many foals ruined by the "keep them ribs" method as the super fat method. Unrefined soy oil works well, or you can get a powdered fat supplement, moderation is key. If you switch to a chaff based diet I guarantee you will see a difference and your feed bill will drop.