Potassium didn't work out too well for me earlier either: http://www.gwern.net/Zeo#potassium
Kind of weird given how people generally seem to regard both potassium and magnesium as good to supplement. Someone mentioned that it might be important to keep the ratio of potassium:magnesium constant (so separate testing is not good) but I dunno how plausible that is.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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