Be aware. The RO formula alone has less Ca than 321 using calnit.
I needed to supplement with a few ml of Calimagic for my coco grows. Adding more calnit is an option but results in higher N than using Calimagic.
Adding epsom is good for adjusting Mg and Sulfer levels if needed.
Elemental PPM compare...
I love growgreenmi, they had it even cheaper a few weeks ago, grrr should have bought it then. I'll get a bag once I'm done with my current grow, I'll start using it with a fresh set of plants in May and do a journal.
www.rollitup.org