Hey @hollyho – actually I forgot about this thread… I’ve been doing a deep dive over here:
In terms of the fertilome, one thing I’d caution that I’ve learned is that MAP might not be such a good idea – though it may be a fine or even a good idea if you go deeper in learning how to apply it. The nitrogen form NH4 can have significant consequences on the root zone pH. It can be ok as an amendment, especially in veg rather than late flower… but I think you’d have to be careful to check runoff pH in coco or soil media or monitor your reservoir pH in hydro. NH4 also has a rapid uptake, so that might not be so great at certain points of the grow cycle.
With MKP, it might not be great in veg but it would probably be ok in early flower. If you are looking for a P supplement in veg, I actually think that magnesium phosphate is probably the best choice, because you can do a slight reduction in epsom and use a little bit of that in its place. Sulfur anion is way overkill in the 5-XX-26 formulas, so you can afford to sacrifice that in favor of some phosphorus. I’d have to run some numbers, but it shouldn’t take much to boost up to 60ppm, which is probably a good number through stretch. I have also had good success sacrificing sulfur in veg for nitrogen using magnesium nitrate. Since magnesium fertilizers can provide all available anion forms, I would make my substitutions there and change nothing else.