I think it depends on your grow method...Mine is set, so I add my 3-part and then calmag, LK, hygrozyme...

but, As I stated above. If you want to set your ppm's at a certain limit, then you might want to add calmag 1st, then take ppm reading...add you 3-part mix until you get to the ppm level you have chosen.

You know you can take a gallon of water and add your nutrients by themselves for this purpose. If you use 3-part then you can mix each part seperately in seperate gallons of water and blend them as needed. I hope this helps. peace