Idk about adding stuff to
promix, I know it's done, but I have never done it. I use strait
promix and strive nutrients. No PH'ing NO checking PPM, just follow the recommended amount with strive no need to do reduced amount. Over sized pot water once every 7-10 days. Easy peasy. I am sure others will know what to do in your situation, but I'm all about simplicity. Nutes a very important part of the grow, adding this and adding that in the soil, then using liquid nutes on top of that seems very complicated. Sorry I can't help just don't have the experience in that area.
As your a new grower if you have issues with that setup, think about simplifying the setup. Maybe you will be a professional soil maker and your plants will come out like 300 LB gorillas, it's just nutes are the foundation to your grow, and you got nutes going in everywhere add in the soil from the garden which you don't really know whats in it.
There are some soil builders in here so hopefully they chime in. Good luck.