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Kinda depends on what you got pulling the air in.
The intake could use a fan also. If you are wanting air to come in that spot then force it by a fan. If you have a fan on your exhaust then air will come in any crack through out your room. This will cause a build up of dust in areas that you don't want people to question. also you cant use the intake to regulate heat. You can get the inline duct fan helpers pretty cheap. What is the CFM of the fan that you are using currently?
Mildew is a bad problem and I have not heard anyone having a fix for it, but...... sometimes the roots will fuzz out because they have way too much water and they are able to make very very small roots to collect water. I hope it is the later. If it is mildew, take the plant out of the room and dispose of, then clean and get ya dehumidifier. Get your humidity to 50-55% and you will be kicking it old school!