Hi, using Pro-mix soiless medium, A/N at 3/4 strength, (which tests out at 5.7/5.8 pH before watering) but my medium run-off is always 6.5 range?? Soil probe says it's even higher, but it's a cheap probe (have ordered a better one) I tested various pH level (non-nute, R/O) water through my raw medium, and whatever goes in, seems to come out basically the same. Doesn't seem like the Promix is causing the increases....??? I flushed 5x the pot volume through these plants, with plain pH 5.0 water (testing after each flush) and I can NOT get run-off lower than 6.5?? Calibrated metre often, tested against known samples, I think my #'S are accurate. Flushing brought my tds/EC down to nothing.....but pH didn't change much. WTF?? What could cause soiless pH to resist change like this? TDS ppm came down to 40 (pH balanced R/O water), but pH remained bullet proof. Brought last run-off sample home, did a fresh pH calibration & 24 hr. later, sample still reads 6.4 I know I am having nutrient lock-out issues, and think this pH is causing my grief. Any thoughts appreciated.