I tried increasing ppm as well and they would not eat. As the foliage got worse, they ate less and less (ppm rising as water level dropped).
Ive seen many grow journals with cultured solutions in rdwc, many of them running co2, and for the most part they follow the schedule and get beautiful results. CS actually shows recommended conditions at different stages along with the schedule and they are showing 1500ppm co2, so they are assuming many will be running it with the nute schedule they specify. The reason i chose to try CS was because after doing a lot of research, i was seeing tons of guys crushing it by just following the schedule. Literally every other line of nutes is a guessing game especially in dwc. Instructions on bottles nowhere near realistic, 2 to 4 times too strong usually. Everyone will have their opinion but to me it doesn't make logical sense that all 4 plants of different types showed same symptoms at exactly the same time because they werent fed enough. I grew dwc for years and one thing that is always a dead give away with hungry plants is ppm dropping as they eat faster than they drink. These did the opposite. I tried feeding less for a while, tried feeding more for a while. Same result, kept losing leaves, plants didn't want to eat. For years i have followed a very simple rule for feeding in dwc that has always worked. If ppm drops, increase feed, if ppm rises, decrease feed. These plants were not asking for more food.