Ok so i have a 5x5x7 tent and i switched over to hps bulb a few days ago and it runs much hotter than the MH. So i have 3 choices run 600 watts and it stays at 75 degrees or run 750 watts @ 80 degreees or 1000 watts @ 85 degrees, My tent has a 745 CFM fan hooked up running at 70% all the time and a 16" fan inside i have good air flow and its constantly pushing the air OUTSIDE my house and sucking new air in. my question is would it be worth it to run the extra 400 watts and have the temps at 85 or should i just run 600 watts and keep the temps at 75 as i have heard this is the ideal temp without C02 Edit: running my fan at 100% is not a option as it is too loud.
75 is ideal without CO2. You can go up to 85 safely with CO2. My room ambient stays about 78-80 and they seem fine. I'd try the 750w and see if the plants get stressed.
I'm pretty sure you're supposed to have it at 85-95 with CO2. Cooler than that and it really doesn't help the plants much.