Calcium is really important but it's often plenty present in tap water, so depending on the hardness of your water, a nutrient that contains it might be overkill.
I think Silicon is another that you are going to want if you have soft water.
I add Silica Blast for both of those.
stinkyattic Reviewed by stinkyattic on . Are Secondary Nutrients Important? Three different types of nutrients described: Primary, Secondary and Trace nutrients. Why are secondary nutrients (calcium and umm.. 2 other) NOT found on any of my fertlizers? They are NU-GRO 20-20-20 and MIRACLE GROW ULTRA BLOOM 15-30-15. They contain all the trace/micro-nutrients (eg. Bore, Zinc). Why is this and how important are the missing secondary nutrients? Rating: 5