I think you're over feeding and over watering them. I'd let them go a day without anything then start flushing your soil for about a full day multiple times then let them dry out, just use water and maybe superthrive for about a week and see how they respond.

Honestly? Keep it simple, I'm not exprienced with some of these exotic nutrients people are using and the schedules they are following, had a friend using the foxfarm schedule and she had all kinds of problems.

I'd suggest after flushing to go very, very light on nutrients at first, maybe 50% of what you were using and see what results you get. I wouldn't use full strength until they are larger and looking healthy. The old growth will not repair itself so watching it for improvement won't help, keep an eye on the new growth and leaves near the top of the plant. I sometimes trim off all the damaged leaves so it's easier to tell if any of the other undamaged leaves are having symptoms. I'm hardly an expert and have had to learn from mistakes due to either impatience or inexperience. It's not as easy as dropping a seed in the bucket and watering it but it's not much more complicated either. I just think people(including myself) tend to over think the process and that may cause more problems then solutions.