If you run it as is you will be essentially growing in a type of hydroponics referred to as "drain to waste or DTW. Same basic principle as growing in coco. You must fertigate every time you water. You can't think of it like soil. I have found that promix hp likes a nutrient solution in the 6.0 to 6.4 pH range and my personal sweet spot is around 6.3. You want to let your medium get fairly dry before watering (one area where it differs from coco) as it doesn't seem to like being constantly wet. I try to shoot for a pot size allows me to make sure they are fully drying out at least daily when the plants are in late veg and into flower. It is really easy to go to big when choosing a pot size for a pro mix grow. As for EC/PPM, I have some girls in mid flower right now and they are being fed daily at about 850 ppm on the .5 scale.
I'd look and see if the nutrient manufacturers have a DTW feed schedule on their website as a starting point.