magnesium deficiency can cause it but that's usually in advanced state of grow.
Foliar feed of epsom salts will correct that.
Dolomite lime contains magnesium.
here's a thread for Aussie growers maybe you'll find some feedback there.
https://www.rollitup.org/general-marijuana-growing/250691-aussie-growers-thread.html
extra dark is no problem, Coleman makes a safe for indoor propane heater that will run for 16 hours on a one pound cylinder. Bearcat I believe they call them. If they get close to freezing they may go into shock but recover.
if yer venting the room during lights on then take it down and store it in the fridge (sealed of coarse) Eggs will hatch later after you kill the living ones so you pretty much have to keep at them 'till you harvest.
I prefer to use Safers Soap until the last few weeks of flowering so that the...