how do you know a cal/mag deficiency?? ive been growing a long time, never used cal/mag, never thought i needed it..but how do i know? what is a sign of cal/mag deficiency?? leaf color, top or bottom of plant,? i know how to see n or p deficiencies mostly.. ive been using gh 3 part, nova, and maxi series for 20 years in rock wool and co-co never had any problems,, but ive been told to add cal /mag.. im not adding it unless i need it, so how do i know?? and what brand of cal/mag would be best mixed with gh nutrients,, it seems every brand of nutes has a cal/mag now.. so wich is best and why...please help me!!