Ventilation check please!

I wanted to ask a question regarding an attic ventilation system. I have a 1000w HPS hooded light with two 8" openings on either side. It is about 18-24" above my ladies. I connected an 8" inline exhaust 755CFM fan to one side and 6" tube duct to the other. I have the fan blowing into the hood to suck air from the room through the hood into the duct and into the attic. I also have a window with a portable airconditioner/dehumidifier attached to it, right now we use it as a dehumidifier which pulls air from outside into the room. We also have a ceiling fan to circulate the air. I was confused about someone saying that the exhaust fan will be pulling air from the attic? We only have one vent leading to the ceiling, so this shouldn't be pulling air back in with our system set up, correct? Also we can't get the room humidity lower than 50%. We were wondering if this was adequate?
We run a hydroponics drip system, 8 plants, 1000w HPS, about 6 weeks into flowering. Any advice will help. Thanks man. Right now it seems to be working great so far! Any advice on controlling smell?

hot air up, cold air gets drawn in from below. sop

The fan will work better when it's pulling air instead of pushing it. Best place for it would be near the vent into the attic, or better yet, in the attic itself. This should help with temps and humidity a little. A carbon filter will work great for the smell if you can get the humidity down. Just be sure to get one that is rated for your fan. You can mount it before your hood so the airflow goes like this:

Carbon filter >>> Hood >>> Inline exhaust >>> Attic

Also the less bends in your ducts, the better your fan will work.