Did the first ES drink taste "not too bad" to you? That was a signal to me that I was Mg deficient. The other thing to consider is whether you have sufficient fiber to push food through. Rather than drinking apple juice, you might consider eating whole apples. They are winners in the fiber area, both soluble and insoluble, as well as having malic acid to soften stones.
I am now taking ES baths as well as Mg supplements. I find that the ES baths are very effective at detoxifying my skin and helping rid me of headache, grogginess, etc. I can't believe how clear and even my skin tone is the morning after an ES bath. Oh, and I now hate the ES drinks as much as others.