Iam having a problem with some of my plants in 4" short blocks on top of Grodan Uni Slabs. The problem plants are 3 and 1/2 weeks into 12 - 12 flowering photoperiod. Visual symptoms are yellowing and dying leaves starting at the bottom and working up. All fan leaves that are not yellow or dead are light green. Inner bud leaves are healthy. Iam feeding a simple 2 part grow and bloom full profile base and recently switched to the bloom after 2 weeks 12 - 12 of grow base. Feeds have been steady between 700 and 800 ppm using the Hanah 500 EC to PPM conversion scale. pH input solution is 5.6 to 5.9. This is a non recovery drain to waste system. Slight trickle of runoff and this is probably where my problems started weeks ago. Apparently not enough runnoff. I just went downstairs and took a big syringe sample from one of the most yellow and dying leaved plants from several spots from within the rockwool slab. I tested both PPM and pH on the test sample (Bluelab Combo - cleaned and calibrated) and return was a whopping 1450 ppm and a very low pH of 4.5. I confirmed the pH sample test using bromothymol blue drops/vial and color chart. It was reddish pink. Any experienced rockwool growers have any suggestions? Should I make up a tank of base nutrient solution (tap water is 120 ppm at 7.7 pH) at 600 to 650 ppm total and no pH adjustment? It comes out at 6.3 to 6.5 after adding the nutrient fertilizer before adding pH down. Fertigate the slabs until slab samples hit close to target ? (5.6 - 5.9 pH and 700 to 800 ppm???)
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