I am feeding every watering with Jacks Part A 4g per gallon, Part B 2.4g per gallon and Silica Blast 4ml per gallon. I am also growing in Promix this grow. I pH to 5.9 - 6.0 and make sure I get plenty of run off. My ppm reservoir is around what the feeding chart I found online says (990 - 1010). The pictures from where I got my seeds from had purple in the buds, but I don't se any at this moment.
I ran Jacks RO formula "1 part" but it actually lacks Sulfur & Magnesium so you still needed to use 1 gram of epsom salts per/gallon of water.
If your using Part A & Part B I'm pretty sure that's their "3-2-1 formula" which stands for 3 grams A, 2 grams B, 1 gram epsom salts. So you might wanna add epsom salts @ 1 gram per gallon.
ProMix tends to acidify, especially with regular runoff as the lime washes out, I would do a slurry test (mix 1 part soil to 1 part water, stir, wait 20 mins then pH it) I bet your soil itself is lower pH than your feeding, say it reads 5.0 pH you would want to feed a 7.0 pH until your slurry reads 6.0 if that's your target.
I'm actually switching back to coco/perlite with maxibloom because I'm realizing promix acidifies a lot and I'm having to play pH games on an every other day basis, also, promix holds water a lot more than coco so its harder to flush out issues with new solution, instead you have to wait for drybacks or you risk root rot/"overwatering".