I bought a 2 oz bag well, more of an envelope of potassium off Amazon for my tomatoes and just got it today. I didn't hold out much hope for getting something that I could see other then maybe with a long count and some statistics. Well I was certainly surprised, my background is about 17 cpm. The potassium gives me 41 cpm... pretty cool :-)
I told my grown daughter about this (she's an avid gardener) and she said "I wouldn't use it" I had to explain all potassium contains a radio active isotope :-)