Negative pressure and high RH?

So I am currently in an on going battle with high humidity. At night times the RH gets to 99%! I'm not sure how long it hovers at that, but just the fact that it reaches that high isn't a good sign! I am running a DR80 (2.3 x 2.3 x 5.7) with an intake at the bottom, and an outtake connected to a carbon filter, running through a 400W HPS cooltube out the top, into the same room. During the day we have the AC on if it gets above 85 degrees in the tent. During the day the RH hovers from 33-50 %, pending on the days. It never goes above 50% during the day though. We have 2 dehumiditifiers in there, and they are pulling water from the air, but obviously not enough.

So heres the question. I've read that negative pressure could have a direct effect on high humidity. Before the lights go off at night, I always close the 3 passive intake flaps on the tent to create negative pressure so it doesn't reek (we live in an apt), but could this be what is making my RH sky rocketing? Some nights it drops to 77%, but thats still way to high.

We got some mold on our last crop, and powdery mildew is already showing on these 4 days-into-flower plants. We just don't want anymore mold or mildew problems.

Has anyone heard about this before? I may try it tonight when lights go off to see, but I think I may just run my ventilation 24/7? I also have the intake/exhaust fans turn off an 1 1/2 after lights out and turn on 1 1/2 before lights on.

Use a dehumidifier in that room. If you mist your tops..... stop. Only water from the bottom.

Thanks for the input.

We already have 2 dehumidifiers in the tent itself. Think I should move one into the room that the tent is in?
Also, I always water from bottom up. Never once have I misted the tops of my plants, ever. I've never foliar fed.

Absolutely...... if you have two, then one inside and one outside.....RH knows no boundaries.....

CrackerJax said:

Absolutely...... if you have two, then one inside and one outside.....RH knows no boundaries.....

Click to expand...

haha, good point. I'll try this as well.

Think I should leave the ventilation running 24/7 too? What about the negative pressure, ever heard of that before?

Thanks!

Intake and outtake..... from where to where? What is the source of air I mean...it's RH.

As for negative pressure, no I haven't heard about it, but a couple of questions come to mind immediately.
How do you know you are creating negative pressure? (barometers inside and outside the tents?)
Can negative pressure be done passively? (without pumps and a perfectly sealed system)