I recently also bought Ca(NO3)2 from Ecocity. I also had some initial confusion with regards to the .4H204. After looking around on the internet, all I seem to find is that the .4H204 is that the the calcium nitrate reacts with the air and absorbs the moisture. Wikipedia has it as "Calcium nitrate, also called Norgessalpeter (Norwegian saltpeter), is the inorganic compound with the formula Ca(NO3)2. This colourless salt absorbs moisture from the air and is commonly found as a tetrahydrate."
Not sure if I'm on the right track, but I simply ignore the .4H2O4 and simply use the measurement on the calculator as it is and its working well for me.
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