Help this happened almost over night.

Help please this is my first indoor grow and first hydro. 18 plant CAP Ebb and Grow 1000watt metal halide/HPS. With light rail 3.5 mover. 165 cfm intake and exhaust fans, Fox Farm nutes. along with beneficial bacteria, and fungi from advanced nutes. The plants all seemed fine 2 days ago then yesterday this extreme wilt started in a few plants, a small amount of yellowing occurred on the bottom leaves. I didn't do anything new to cause the wilt but after it started I flushed the whole system and refilled with fresh water and nutes, been changing res every 2 weeks. Thank you for any help. sorry pics are off cell phone.

Also the strains are The Purps and God Bud, there are other plants in the garden but they don't seem to be affected. Please I dont know what to do and this is all I have.