first grow, co2/ventilation questions

Yea, the air is being constantly renewed. But by the looks of it my current setup doesnt need the ventilation I have provided, I built it planning to use a HPS or one of the other light types which gives off alot of heat, which I will likely add in the future. So for the time being I wont even bother with the ventilation and plug the vents, ill buy a small desk fan to place inside the box for the air to give the plants strength, this way I can keep co2 levels constant without much effort.

Thanks soo much for the help guys its a great community here that im glad to have found, hopefully one day I can help people in my current situation

So what kind of light you using???Your plants won't be able to utilize the extra Co2 if you don't have strong enough light source.

Im currently using a 250w CFl (6700K) 8U bulb, but im planning on adding more shortly. Might go for a lower temp (2700) and add them in for flowering.

Got my first sprout today, serrated leaves within 6 hours :O

Only issue I have at the moment now is that my PH is a bit high, I thinkit needs to be about 6.5, but its 8 so im looking into ways of lowering it. Will have some pics up soon.

Buy ph down 5.8-6.5 is ideal.That lighting alone is not enough,you will actually be wasting most of your Co2,I mean if you get it free or make your own thats fine I guess but non the less still a waste,remember 1500ppm is ideal 4000ppm is toxic to humans.I only use Co2 in my flowering room.