Final result: it negatively affects my sleep, d=-1.1. For comparison, most improvements score less than 0.5.
See http://www.gwern.net/Nootropics#potassium
http://www.gwern.net/Zeo#potassium
If I were to do a followup experiment, it would be blinded & randomized as usual, with consistent doses (eliminating objections 1-3), but more importantly, the dose would be consumed upon awakening. It is highly unlikely I will bother with a followup experiment. Potassium is not of particular interest to me, my existing supply is low after months of consumption, I observed no subjective improvements on consumption, and so I am not inclined to run the risk of damaging more months of sleep.