Tam,
7 days between waterings at this stage of flowering seems to me to be a bit too long? I'm watering every 4th day, maybe 5th if pot is not light enough but I couldnt go 7 days! Are you sure they are not drying out too much? For comparison, last grow at this stage my grow diary (yes, I'm a sad bast**d who writes it all down!!!) tells me that at 6 weeks 12/12 I was putting a litre of water through each pot every 4th day. This grow I'm doing a little less, maybe 700ml each watering....how does that compare mate?
Nutrients: again last grow/same stage 2ml bio bizz 'grow' (for the N) plus 2ml of bio bizz 'bloom' plus a blob of molasses per 2 litre bottle water PH'd down to 6.2/6.4 range. Now depending on the look of the plant I would then dilute that bottle further with plain water as required.........hope that make sense? I would say they need a good feed tam, but don't overload it too strong. At around 6 weeks 12/12 I would also introduce a single shot of canna PK13/14, just a one off shot.
I'd look at your watering/feed regime mate? Other than that not much can be done about the cold BUT they are budding up well still, as they do
If you need to add N fast seaweed is brilliant, I have done entire grows start to finish on just what I picked off the beach here at low tide, seaweeds, kelps, cockle and mussel shells etc etc, all stuck in 2 litre bottles and given a good shake up, after a few days it STINKS, but man do you get healthy green looking plants! You have to watch your salt build ups though, but it was never a problem apart from my skin allergy to certain sea foods, were it not for that I'd still be growing that way ;-(
Hope this info gives you something to think about mate, you're still going to get some nice buds though