At what ratio do you mix the MP fertilizer with the MC?
It depends what your target P is! I don’t use Mega Crop, I make my own mix of stuff by doing the math necessary to figure it out.
I target N at 200 and my current formula’s N-P-K is 10-8-14, from beginning to end, not far from MC, so I would just do the math to bring the P up to 8. Excess K is rarely a problem (at least in hydro) unless it is way off the scale, so I don’t sweat it too much, but I do calculate all the things rigorously when I make new stock solutions. I can post my current recipe, if you like.
You must learn to do the maths, it is sort of a pain in the butt at first. I could calculate a dose with MC for y’all...give me a bit. I actually forgot how high the K is in Mega Crop, maybe that’s pushing it to add MKP, I dunno, but most P boosters in the market have a fair amount of MKP in them, from what I have seen, I bet it would be fine.