@Jhef weren't you growing in RDWC or did you change that plan? Fun thing about coco on commercial scale is buying and throwing away coco. Make sure you get the pre washed stuff. On a commercial scale the RDWC plan you had is really sweet because of the man hours wasted just handling any potting medium. Even unwrapping rockwool and having to throw it away after harvest is work compared to filling a reservoir with a float valve and draining the system by opening a valve lol. Just something to consider. Great plants can be grown in coco. I had major issues with RH% when I ran coco, never could figure out why.
When I did coco with GH and RO water I used calimagic at 5ml per gallon and also added some epsom salt for more magnesium, as I recall it was 1 gram per gallon in veg and 1.5 grams per gallon in flower. Thats what worked best for me with coco and RO water.
I will note that I like the calimagic because it has less nitrogen than other cal mag products I have used.
If you start to see signs of a mag def you should make sure that your pH isn't too low. Just a couple points low can cause magnesium uptake issues. Another thing to note is that when growing in a medium like soil or coco, sometimes the pH of the root zone is not the same as the nutrients. I ended up having to water my coco with a little high pH because the coco pH was trying to drop on me.
FWIW none of the commercial growers I consult with currently use coco. Some are soil growers, organic style and some peat based soiless mixes but most of them are running hydro, Flood and Drain for sea of green and RDWC for trees/plant count being the popular choices.
