Adding Fan or changing light ?

Hi, I just buy a tent 2*2 *74
I installed a 400 watt MH and I m using a drip bucket System.
My exhaust fan is a small fan like PC but on 120v.
I am using a canfan 4" as intake. The ducting is about 24 feet long .... maybe I am loosing fresh air ?? :
The temperature is more than 86F
Would you recommand changing my exhaust fan for something bigger like a canfan 6" or simply changing my lighting for T5... as the price is almost the same.....

t5 works great and saves on cash for the electricity bill

Pictures would show more. If you can .
Also worry less about the intake and more about the OUTTAKE> get a stronger outtake. at least a 4" there some formulas to figure out exactly but bla bla bla. Your tent seems on the smaller side so a $" fan should do. Keep it going 247. Water early in the Day. also if Veg then MH is fine but and a HPS is best for flower.
GEt the fan not the light.. OR maybe an Aircooled fan are best... if you dont have that already.
AS for the Ducting... Is it new ? If so then should have MINIMAL holes

I check with my local hydro store, and a 4" fan is 200$ and I didnt found a 2 feet long t5
Can I use a Single t5 ( like what I use for cloning ) to grow my mother plant ?


*****
After doing my homework, I finaly choose to try CFL instead of T5.... Cost seem lower with CFL....
Thursday I will setup all