Sorry, dumb of me not to put that (it was on another post).

ph c. 6 - 6.5
Humidity 20- 30% (too low)
Temp 25 - 30 oC (too high)
Ferts so far : small amount of ammonium sulphate (N) in veg and small amount of Fishblood/bone (5-5-6.5) during flowering (c.10 days in under 12/12).
Couple of more pics attached. Thanks for the link also.
I still can't decide if it's N an deficiency, or lack of P during flowering. Magnesium and subsequent nutrient lock does sound plausible as I haven't given't it any Mg. In one of the pics, you can see the other plants looking fine (although their lowest fan leaves are starting to droop and yellow).
Anything else I can help with let me know (there may be some more info in my other post on indoor growing msg board "Advice welcomed")

Thanks for taking the interest and your time.

Cheers.