Hi monty,
I use a hose-end sprayer, and it works really well--but I use a baby shampoo/dawn mix with water. I have never used the powder form or supplemented with kelp, humid acid, yucca, etc, so I can't advise for rates.
For baby shampoo, the general recommendation is about 3oz/k, but there is considerable leeway.
You may really enjoy mixing this stuff yourself. If not, I've looked into Aerify plus and Nitron A-35 as alternatives. They seem reasonable and convenient to use, if somewhat pricier than a homebrew.
You might want to check out Grass Daddy's youtube videos on this subject. I'm not sure that he specifies mixing rates in the videos, but the videos will be a great introduction if you haven't done this before (I'm making some well-intentioned assumptions here).
https://www.youtube.com/watch?v=U0SmPEeH27Q
https://www.youtube.com/watch?v=ztKl1LLiSLE
https://www.youtube.com/watch?v=shpChsHTq5Q
https://www.youtube.com/watch?v=j-ze0KvNPho
Also, be sure to wear a mask when mixing the SLS. I've read that it is a serious irritant.