i believe adding co2 will eliminate a need for constant exhausting, most people are exhausting to get rid of odor and for those who dont use air cooled hood to get rid of heat and humidity, the co2 will allow you to run higher temps, now you say you want to add a carbon filter? no problem, instead of ducting out the fresh air, just leave the filter/fan with no duct, it will "scrub" the room air without needing to make another hole in the wall, also you wont need to bring in fresh air into the grow room, so theres another hole in the wall and fan that you dont need. have an air cooled hood and co2? no problem, just creat a hole in the wall for fresh air intake that runs thru the fan and into your hood and out the room thru an exhaust hole, this way the grow space air isnt effected. the way you have it running now is just fine for your setup, the most economical way of having a setup with carbon ffilter involved is haveing your filter attatched to yourfan, sucking stinky air thru the filter and blowing it throu your hood to cool the light and out the room, this method knocks out 2 birds with one stone, but you will need at the very minimum an intake for fresh air to provide what little co2 comes in with it and also for colling purposes, but you will find using this method that your co2 can is gonna run dry very soon, so if you want air cooled hoods, carbon filtrtation and co2, i advise you to get a 2nd fan just for the lights and let the carbon filter run periodically to preserve co2, its obvious you need to run the fan all day to cool lights, at this rate you can blast co2 and the plants wont get any cus it gets sucked out so fast. you can figure out how long to run co2 with the calculator and if say it says to run for 30mins daily, run it 3-4 times for shorter periods directly after your filter runs, your question about should you add it? its not necessary but, if you want to take it to the next level and depending if you have decent harvests it just may pay for itself after your first grow, depending on scale of grow, but heres the double edged sword, you dont want those crazy high temps if you run hydro, if you were in soil no need for a/c let that bitch get up to 95