advice needed on ventilation please,

hi, im on my first effort, and have found this forum great for advice, and with that advice have so far come along quite nicely, unfortunatly my girls have seemed to hit a wall and ive a feeling its to do with air, they are about 2 ft and are acting like they need water, ie leaf droop, theres no sign of any real burns or anything and they are a nice colour, they are watered and fed regulary, this has happened since theyve gone past the 2ft mark, ive just put them on 12/12 2 days ago, but feel my girls need beter enviorment control, heres a brief outline of my set up, 2x 600 hps cool tubes with own fan, a ruck type fan 700 m3, 150mm, rhino/phat 150mm c/filter 600m3, basic fan speed controler and a couple of osciliating fans, the size of space is 2m wide x 2,7 m long by 2.4 high for intake i was on passive but have added a 270 m3 intake fan and still a couple of passive holes! what im worried about is how do i work out if im leaving enough air in the room as ive the extractor turned all the way up and by my very infant maths feel i may be extracting too quick (if poss) i have no heat issues and run the room about 27c, ive 9 girls and would like to keep it that way so any advice would be much apreciated, i have tried to read as much as i can but it seems that most of what i read is regarding temp, and id like to learn how to grow before i try the co2 route!!
thanks cozz

how often do you water? how often is regularly? those symptoms sound very much like over watering. remember, overwatering is the no 1 misdiagnosed problem with homegrown MJ and the no 1 cause of death to homegrown MJ