Just an update on things.
I have been playing with the chem-gro 4-20-39 stuff and have found that this mix seems to be the best so far with the experimental coco mixes:
#'s in Grams Per Gallon
Magnesium Sulfate (Epsom) = 2.0 (may be able to lower)
4-20-39 = 2.5 (3 was definitely too much lol)
Calcium Nitrate = 2.0
I think the manufacturer recommended amount of epsom would probably be great unless using the coco, in that case a little bump from 1.33 to 2 grams per gallon seemed prudent. I am not sure that much is required though with my medium mix having a lot of perlite and vermiculite. I may try easing it back a little as I continue tweaking the mix.
The biggest thing is pH, in my veg room they have been getting a higher pH around 6.8 and they seem very happy. I tried using 6.2, 6.0, 5.8 on different rows and they seem to want something different so the last feed I did half the plants at 6.8 and the other half at 5.8. Will see how they react. I suspect I will need to feed high on the pH and that definitely seems odd but what they want is what they will get. Still tweaking and tuning for the medium but my being lazy and not ph'ing in the veg room seems to have pointed my in the right direction (up).
Once I nail the pH down to a finite number I will start trying to ease off the Epsom a little to find where it really needs to be, maybe I can get it down to 1.5 grams per gallon since the mixes I am running are < 50% coco.