What's more important? Air intake or air output? Help!

I have a 6 foot, 3 x 3 grow tent in my room. I'm using a 400 watt hps light and I have one fan with a flange to put on the tent. I was wondering if I should have it blow air into the tent or blow air out of the tent? What's more important? I also have a small fan that just sits inside the tent that blows the air to move it around. I had it set up to blow the air out but now my plants have what looks like calcium deficiency and I hear that it might actually be no fresh air coming in? I don't know what to do

have it blow air out of your tent and use a passive intake to draw air in

What spanks said - suck/push air out of the tent - it will create a vacuum that will draw air into it.

If I have it blow air out and just open one of the extra vent ports (without a fan, just leaving it open), would that be enough?

Bones987 said:

If I have it blow air out and just open one of the extra vent ports (without a fan, just leaving it open), would that be enough?

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yes make sure the hole is not too small or the tent will go in to heavy negative pressure like putting a bag over your mouth and sucking all the air out, if you can get slight negative pressure inside it this will stop any smells leaking from the tent to your house, and blow the air outside. if you make or buy a carbon filter that will stop any smells being detected outside by passers by.