What's up with that.

A picture of the whole plant without the lights over them and some more info on your setup may help others to better diagnose your problem.
 
That would be magnesium deficiency. As much as I hate the fast answer thing I would get some cal/mag. JMHO Good Luck.
 
you wont be able to get sound advice without more info...soil,..temps,....feeding schedule,....how much during feeding,...days into flower,...p.h....the more info the better the diagnosis
 
Mg shows first on the lower leaves, coz of the curling and leaching I'd go for potassium (K). Also N
 
Were in 7 gal all organic in a 4x8 hut with 2 600 watts on super lumens. Temp 26 to 28. Ph is good only using bat gauno and molasses. Were into day 40 flowering. Tea once a week. Thanks.
 
In Jorge Cervantes Bible it describes everything your picture shows...including an illustration of Magnesium Deficiency.
 
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