I've settled on two for now but still not sure if it's right?
Any advice would be much appreciated.

Thanks mate, two open seems better than one at the moment as one on its own causes too much of a kind of wind vortex and was stressing the smaller plants. With two though it seems fairly stable. Thanks mate!2-Scoops wrote: ↑Wed Oct 06, 2021 1:16 pm1 or 2 should be fine, i run a passive inlet myself in my grow cupboard. I've always gone by x1.5 to x2 times size passive inlet hole to your extraction fan, but i see your running oversized gear. But yes i would think 2 is more than enough in a smallish grow tent.
Negative pressure isn't all it's cracked up to be - it makes no difference to the plants and is really just about making sure that the smell doesn't esacpe before passing through the fan and filter.