Well here'd be my guess...bloom boost overdose.....major league. I'm only saying that because I'll bet your plants were doing fine before it and now look half dead. And ARE half dead I think. Whatever the last thing you "changed" or "added" and then your problems started is where the problem lies. And I'm thinking its the bloom boost.

What to do? Flush. Do you have something like FloraKleen? If not then straight ph'd water and that's all. If you leave them as is you're most likely going to have a bunch of crispy nothings in a few weeks. You may feel free to disregard this advice (please...... because I have a feeling those may very well be done already.)

I cannot offer you any more tips since besides the photos and the mention of coco I can't get much more info out of you except that "the levels seem ok" Without some clear numbers and names of what you are using. I'm just too afraid to guess.

Good luck.