Need Help! What is optimal Co2 levels for my Sqft

hello i have a 9x9xh8 closet with 3 600w hps, air cooled by 6inch vortex, exhaust is 10inch vortex(turned off during co2 time), lumatek digital ballast. sentinel cppm4 co2 controller, and 20 lbs co2 tank. my question is what should i have my co2 setpoint at according to my sqft of 9x9xh8 grow space. does any one know??? plus rep if you can help!

Here's a co 2 calculator, hope this works for you. Good luck.
http://www.hydroponics.net/learn/co2_calculator.asp

That all depends on the regulator, however 1500 ppm's is what you're looking for. Just remember the exaust fans must be off or compensated for.

1500 for sure. Also keep your temps around 85 to maximize respiration and utilization of co2.