I’ve got a 2x2x5 tent and 4 inch inline duct fan (205 max cfm) outside the tent, pulling through about 2 feet of ducting and into a 4 inch ac infinity carbon filter. I’m just wondering what I need to do as far as opening/closing ports. Chatgpt is telling me to just leave one 6 inch port fully open and run the fan on a speed of 3/10. Will allow for adequate airflow/co2 exchange while keeping the pressure negative? The lower I can run the fan the better - I’m in the seedling stage and keeping humidity high enough has been tough, even with a humidity dome
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In general the more airflow the better. A breeze across a plant will help strengthen stem structure.
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I would prioritize climate (Temp and RH) to air exchange. As seedlings, they require a very minimal air exchange. I do however like to keep a Circ fan moving the plant a bit to keep it’s stems strong and healthy.
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I do have an oscillating fan blowing in there. I’ve got it on the lowest setting just to help keep humidity up.
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Follow up question just to avoid having to make another post: I’ve got a humidity dome on the seedling made out of a cut up gallon jug. Light is 12 inches from the top of the seedling, and without the dome it’s getting ~200ppfd. Do I need to turn that light higher to compensate for the humidity dome being there? It is a transparent dome but I don’t know if it might be interfering.
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I’ve wondered the same thing. You might bump the PPFD up a little but i think youre probably ok there. If you notice her stretching more than you care to see, you could increase it a little. 
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Thanks m8. How tall would you like to see your seedling a week after sprouting? I know there is a lot of variation, I’m just trying to get an idea
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I personally like a little stretch in my seedlings so later and hopefully, I have a little more clearance for watering. 2 to 3 inches after a week and as long as they support themselves, I’d say is good. 
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That’s kinda what I thought. Tomorrow will be a week since sprout and it is 1/2 inch tall
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Air ventilation at seedling stage isn’t as important as temp/humidity is. Negative pressure is to help odors from escaping which isn’t necessary for seedling stage. Whatever ventilation settings gets you to a good temp and humidity then you’re good to go.
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That right there 
Temps and Rh it’s crucial for the seedlings.
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So if fully closing up the tent keeps the humidity up, should I do that at the expense of the airflow. My current problem is all of my humidity sensors are giving me wildly different readings. I had them all calibrated two weeks ago, but yesterday 4 different probes gave me readings from 40-80%. Not sure what’s going on. I’m going to calibrate them with the saturated salt test again and hope for the best. For now I’m just kind of pumping humidity and erring on the side of more rather than less