Bigbud RDWC start 03.02.18

It's definitely nutrient burn. Ever heard or read the expression "burnt to a crisp", just like your "crispy leaves". Your nutrient solution is really high for the veg phase, dial it back to 1.0EC/500PPM, then when you switch to flower ramp it up slowly up to 1.4EC/700PPM.
The low humidity might be causing your plants to drink more water, forcing them to take more nutrients than it's safe for them, if you can't rise your humidity, use a lower EC/PPM than normal

The hey are still showing signs of nute stress. With the hooking leaves (nitrogen) and the large spots on the leaves ( phosphorus). I don’t know if this is from before or current so I’ll saythis when you have a nute burn you burn the fine root hairs which is where your nutrients are drawn into the plant first. Usually leaving the main part of the root to do all of the work ( which is where the water is pulled into the plant). It takes a while for these fine root hairs to grow back so the plants will appear “stuck” if you’ve made the appropriate reductions in your feed regiment then they will grow back and the plants will recover within a week or so if not you’ll need to back the nutes off some more

Hi there, what a lovely scrog! Yes harvest is near but you still need to wait a couple of days, your trichomes are currently clear and thin, they must become fat and milky, then you'll know you're in the perfect harvest window. I'll be around, keep us up-to-date, and good luck with these beauties!

Its a combination of potassium and boroN deficiency, the LEDs ain't helping either. Its sapping the energy the plant hasn't got the fuel to keep up with. its affecting the biggest as they demand more feed as they are bigger and closer to the light by a few inches? if they are closer led par would increase. This Would stem from a pH issue or simply underfeeding the bigger girls. Check your hydro system, flush with pH and nutrient solution. Increase feed. Also increase light off temp, this can affect uptake of nutrients.