IT really looks like you are running your temperatures too high or your ambient humidity too low or both. It's that time of year, ya know? The air is really dry.
Rinse that salt buildup off your leaves, give the plants a nice light mist with SMC leaf shine (safe to use up to day of harvest- it's coriander oil), control your temperatures.
If the roots were brown I would say it might be a res contamination problem but healthy roots mean you are cleaning well enough between runs so no worries there.

Edit: One other thing I thought of is that it is a time of year when freezing and thawing leads to snowmelt and runoff, so your water chemistry may be different during the spring thaw- diluted by runoff or even polluted by road salt, depending upon its origin.
stinkyattic Reviewed by stinkyattic on . HELP?? This is a first for me in the 4 years of growing. Some of my leaves started turning yellow and spotting in 3rd week of bloom and today the leaves on the tops of 70% of the plants started to curl up. The PH is 5.7-6.2 and PPM 1400-1600. Room temp 80-85 when lights on. Using GH products and have been doing the same feeding all along with no problems. So I flushed system and filled with fesh water and no nutes. Going to see for a few days if they recover. Any suggestions would greatly be Rating: 5