If you are using a fan as an intake, and it causes your tent to balloon out, then your exhaust fan isn’t pulling enough air. Most growers don’t bother with intake fans, we just use a suitably sized exhaust fan and open up ports at the bottom of the tent to use as passive intakes.
The vent intake that i connected the ducting to was way more powerful then my exhaust fan inside. The fan I have inside the tent is a 4" 110cfm.
The vent was blowing almost twice as much as my exhaust
I'll have to measure the airflow in that vent and then buy a stronger exhaust if I'm gonna use it as an active intake.
Maybe I'll just move everything downstairs and fix something to block the lights from my window when I open the tent.
Too much hassle up on the loft.