Not Flowering properly nearly week 5 - please help!

Hi Everyone,

This is my first grow. This is Sensi Seed Big Bud from seed, i am 4 and half weeks in to flower and i think i am vastly under feeding looking at the bud size at the moment?!

Can some one please help put me back to the right track and explain in simple terms what i need to increase going forward?

600 Watt Hps

60% humidity - Can get a dehumidifier if needed?
70-80 F in day
50F during night

Always PH to 5.8

15 litre airpots
Using Dutch Pro Fertz - They are due a feed today...
http://www.dutchpro.nl/images/kweekschema_hydro-cocos_print_Engels.jpg

8 litre water mix containing:
30 ml of A
30 ml of B
8 ml of Multi Total
4ml of Explode
Feeding 2 litres to each plant every two days.

Please Help! Thanks a lot!

how long was veg time? I think it's looking pretty good. If you did a short veg then I wouldn't count the full 5 weeks as flowering. I think you can let them dry out another day or so with that size of pot, and that also should lower humidity some. But I think your biggest problem slowing it down is the night time temp, 50 degree F is way too low IMO, at the lowest I'd keep it about 65 degrees.

You really have to give us some lights-off pictures for an educated reply.