gotta bring it up a bit you could potentially be having nutrient lockout due to low PH. Initially I thought you were in soil as well. Try calibrating your meter with calibration solution that is an easy culprit to deal with
Maybe give her a nice flush and come back with some calmag and maybe try to water at 6.2-6.4 for just a little while and see what end of the ph range is getting locked out. Ca and mg uptake at opposite ends so sometimes it's beneficial to let the ph bounce back and forth between 6 and 6.4