You will need to add either dolomite lime, or garden lime, or sweet lime to the promix. Just NOT hydrated lime. Otherwise you will experience pH problems from the acidity of the peat. ~$5 for a 40lb bag at Lowes or HD or most garden centers.
I make my own mix using peat from the same co that makes promix (Premier). It's good stuff. I also know that some of the PM's have lime added. Good as far as it goes, they just don't add enough for an entire grow.
Wet