Promix tends be a little on the low side both micro-nutrient and pH wise in my experience. If the only difference between your mix is the lack of compost that's most likely what's at fault here. Regardless of all the soil mixes on here, if your old mix was doing great, go back to it. It sounds simple as you can get. Don't mess with what works.
I personally add compost, dolomite, perlite and a handful of whatever else I have around that looks fun to my promix, but really it's mostly promix & compost. It works great, the plants love it, and I have few if any nutrient problems with it.
Cooking Oil Made Complicated
legitimizing pot hasn't created more users; it has just produced more annoying ones, who now apply Whole Foods--ian levels of snobbiness to the differences between Hawaiian Sativa and Humboldt Indica. -Time Magazine.