What if there’s too much air coming in and not enough going out - read reason below

Maybe connection site is not tight enough or something stuck in connection duct?

4" fan typically maxes out at 170cfm ... i misspoke. as i said, better to buy a fan you can run at 50% power -- whatever the needs calculate to be.

filter sizes generally match the power of that size exhaust fan, but not always.. 4" carbon filters typicalyl should be run at 170cfm or less, give or take. This is roughly what a 4" fan should be -170cfm give or take. Bends in ducts reduce this and any other sort of friction. i'd assume that's the input threshold for the filter, so the 25% a filter likely reduces CFM is after that fact. so, if you hooked a 6" fan to a 4" carbon filter, it is possible to reduce effectiveness of the cabon filter with too much air flow. if you buoght one of those generic fans, it may just not be good with static pressure. There's CFM than CFM @ a particular static pressure.. The curve displaying this relationship is much different in some fans than others. TerraBloom is an example of a high quality fan that's worth the extra dollar. Handles higher static pressure and maintains a good CFM longer into that curve. If you have too many bends and silencers or whatever, that reduces cfm significantly.. Always buy a much larger fan than what is needed so you can run it at 50% to reduce noise and extend life of the exhaust or intake fan. if passive intake, you need 3-4x the area of intake ports compared to area of fan port. otherwise, this too will stress and reduce CFM with more resistence if the intake vents are too small. So, it depends on your fan's ability to push through static pressure, ducting choices, filters, intake .et al... for some resulting CFM at the end that needs to push the same volume air that the tent holds per 2-3 minutes. that doesn't mean it refrshes 100% of the air in 2-3 minutes. just a simple check to make sure it's enough. it'll take longer than that in reality for 100% refresh.