ok i have never actually seen this before as a problem somebody actually has, what are your temps im gunna guess they are running on the cold side most likely at night, its something called MOLYBDENUM (MO) ill type it word for word in the garden saver book i have by j.c stitch and i quote:
HOW COMMON IS IT?
MO deficiency is very rare, but is more likely to occur in color-changing strains in cold temp conditions .
SYMPTOMS:
The middle leaves turn yellow. As the deficiency progresses towards the shoots the new leaves become distorted or twisted. A MO deficiency causes leave to have a pale, fringed, and scorched look, along with retarted or strange-looking leaf growth. Older chlorotic leaves experience rolled margins, stunted growth and red tips that move inward toward the middle of the leaves. Somes MO deficiency is misdiagnosed as a N deficiency. However N affects the bottome leaves first. MO affects the leaves in the middle of the plant first and the moves up to the newer growth. Excessive MO in cannabis looks like FE or CU deficiency.
MOBILITY:
MO is mobile.
ROLE IT PLAYS IN PLANT NUTRITION:
MO is contained in enzymes that help plants convert nitrates to ammonia, which is required for protein production.
PROBLEM SOLVING:
Foliar spraying with water-soluble fertilizers aids in overcoming the deficiency. Because plants need MO in such small amounts a hydroponic micronutrient mix is often the most efficient way of supplying it. These ferts can be used as foliar sprays or applied directly to the soil, as well as their customary use in hydroponic nutrient solutions.
GENERAL DISCUSSION:
Generalls a MO deficiency occurs when S and P are deficient. MO toxicity does not tend to wreak havoc on plants, but excess intake causes severe problems in humans so extra precautions should be taken when using it. "
well i would recomend looking it up for yourself but that sounds and looks exactly like what you have hope any of that info could help you and good luck with your problem any other questions let me know.