I’ve been growing with promix for my last 4 grows and Promix needs about 20% run off when watering and is more like hydroponics than soil. The ph of promix can drop below what you want some use Dolomite lime to help balance the ph out in promix. I personally do not do that. If you water to 20% run off every time you know what ec/ppm and ph your putting in and what’s coming out. If your ec/ppm or ph is high or low when it comes out take notes and either feed less or feed more depending on what you mediums ec and ph is. Checking your run off can help you know if you have to much salt build up in your medium. I think you either have a low ph problem or nutrient lock out and nute lock out can look like a nitrogen deficiency. Taking notes of everything is going to be your best reference of going back to for problems that occur. I personally feed feed water when it comes to my plants. When I’ve been feeding with nutrients I have not been watering to run off but when I use only water and cal mag I water to run off so I get that salt build up out where nutrient lockout comes in to play. Every strain is different and some will eat like monsters and some need barley any at all. Let me know if you have any questions