Looking to get co2. Need advice.

3 tents, all 4'x4'. All air cooled hoods. Air comes from the attic on one side of my house, and is expelled to the other side. 2 tents have a 1,000watt hps bulb (the ballasts are switchable and one will be going back to MH), and one has a 400 watt hps. I also have a closet with a few small plants in veg under cfl and a clone bucket. I have a 6" centrifugal fan pulling air from all 3 tents and scrubbing it through carbon. The room is not sealed yet, but it has no real ventilation. Just several fans moving air around, and no door on the room.

here is what I want to do:

Seal the room, put an air conditioner in the window set to about 85*, and supplement co2.

So I think I want something that will measure ppm of co2 and release it that way rather than me guessing at what the concentration will be over time, or measuring it with a kit to dial in. Especially since the conditions of the grow will be changing; I don't want to sit around for half a day measuring ppms with a syringe to redial it back in when I switch one of the tents, etc. I think a monitor that does it automatically will be much more useful.

I also want to consider future options though. If I can dump my scrubbed exhaust into the attic rather than back into the room I could reduce the temp (when the ambient temp is not quite hot enough to justify an air conditioner, but the temp in my room exceeds acceptable levels). This will require coordination between my co2 and exhaust though so im not just dumping co2 into my attic.

What equipment does everyone recommend?

I don't want to spend $5,000 on a super state of the art system, but i don't want to cheap out. I want to get the job done right and I have a decent amount of money to invest, especially since this will hopefully be a permanent solution I will use forever.

I bought a digigro coco co2 controller monitor and a regulator on eBay for $350. Bought a 20lb tank(filled) locally for $135. Also bought an greenair atmospheric controller for my cabinet. The digigro automatically keeps the ppm at 1200-1500. It is working killa for me. My cabinet isn't sealed but I do have a backdraft damper on the Intake and it seems to be sealed pretty good. The atmosperic controller is running the show and doing a killa job. Probably couldnt do it without the greenair or something comparable! Been running co2 almost 2 weeks and have a reading of about 50 on the gauge. My cabinet isn't that big so the output of co2 is at the lowest I can get the regulator to go. I am very pleased with my co2 setup!

i too bought a digigro they are top notch people and go out of there way to help. but i run mine with a water cooled co2 generator(also known as a tankless waterheater)the monitor was 279 and 120 for the heater and 80 for a pump then addeda 55g resand off i wentdownthe road of co2 filled dreams and I"M not looking back. for more info about this check out a thread called "well fuck n.a. i got a tankless water heater"