First thing I thought of when I saw the leaves was H2O2 burn. (still green but crispy leaves) Also looks to me like ph swing (canoeing and twisting of the leaves) and overnute. (browning and leaf margin upturning and slight browning) With using the coco, do you use CalMag or something similar?
Wish I could help more, but I have no hands-on experience with hydro or coco growing. (might I recommend some peat-based soil, lol?)

Takes about three days to see anything positive. Bad shitcan happen overnight.

If this is happening only on the one plant, perhaps it's needs are different than the other two. (different strain?) I'd keep doing what you're doing on the two that are fine...and perhaps lower nute strength on the problem child.