Well... I decided to take drastic action this morning. Took the nute solution from the res and brought it up to 1.6 EC using the Remo nutes but going a bit heavier on their micro, top fed a couple of litres through the pot and then filled the res up with the remainder. Just checked on it now and there's already a big difference. In the picture of the two plants side by side in my previous post you can see the light green plant's leaves are a bit droopy. Compare to a picture I took just now.
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They're up and praying to the Gods of Cobs. I swear she'd grown a couple of cm's as well. So maybe she's just a heavy feeder and I was starving the poor thing. Fingers crossed this is it.
good to hear sage, and wise to spot the tip roasty and back off some, or a lot-- 3.0 EC=1500ppm ! yeah, some plants just never deepen up,.. my Purple TrainWreck is like this, after trying a few things,... no point in forcing it,... Nice job on steering out of that skid mate! 
finish well!
