Hugh ph swings point towards bacterial infection. I run DWC and a RDWC at 500-800ppm in veg and 1000-1300 in bloom with no problems. It’s not your airstones. If your ppm is changing a lot too maybe it’s just what your plant is eating out of the water but even when my plants are eating 80-100ppm...
I typically run 500-800ppm in veg. And 1000-1200 in Bloom. Change Rez every week. Deff use cal mag with RO water. I top off every day and add back nutrient back up to the ppm I’m looking for if needed. I’ve been getting a GPW+ out of a CC rdwc system this way. Shooting for 2gpw this round...