Some of my plants leaves are turning yellow with the tips turning brown. Does anybody know what this could be from? They were in 4x4 rockwool cubes in an ebb and flow flood tray receiving about 1100ppm nutes. I had lots of these plants receiving the same light, in the same tray, with the same nutes, and same flood time but only a portion of the plants started to yellow. The rest of the plants are healthy and lush green. My water is always at 5.8 when the plants are in cubes. I recently transplanted into coco. I'm going to foliar feed today with Thrive Alive B-1 (red) to see if that helps with the yellowing. Any help would be happily received.