While it's true that Calcium nitrate is hydrophilic and likes to soak up water as it sits, this generally isn't a big issue unless you live in a damp climate and don't keep it in dry storage like ziplock bags, or airtight containers. I DO use them both by weight; I measure all my materials dry, in grams, and pour my Jacks and epsom (plus amendments that do NOT contain calcium) into one 5 gallon bucket, and my calcium nitrate (and anything else I'm adding that contains calcium) into another 5 gallon bucket.
The point I was making above about ratios is that if you want to run 3g/gal of jacks and 2g/gal of cal-ni, then you always mix them for the same amount of solution, such as 50 gallons;
3g/gal of Jacks x 50 gallons = 150 grams
2g/gal of Cal-Ni x 50 gallons = 100 grams
2g/gal of Epsom x 50 gallons = 100 grams, this goes in the Jacks bucket ONLY!
I fill my buckets first with a gallon of warm water to dissolve the nutes, stir until all the granules vanish, and then top up with cold water. Only then do I pour this mix into a reservoir with cal-ni or anything else premixed in it. I haven't had any trouble with nutrient lockout at all if I do it this way. Now, pour all these, once thoroughly mixed, into your res or wherever. It is only at this point do I use my EC pen and check to see where I'm at with solution strength. As a starting point, you always want your solution strength to be low; so mix somewhat less than your total capacity, and add water until you get to the EC you want. To raise EC, I generally make a mix of 20 gallons' worth of nutes (in my two 5 gallon buckets), then add it to my RDWC, and then only dilute once it's throroghly mixed into the system. Then, I know how much water to add to bring it down to where I want.
