So at veg stage lights at 18/6 with just fan inside running at 24/7 and at flower stage lights 12/12 with both fans running that's carbon filter and fan at 24/7 also is one fan enough for a 120x120x200 tent or two thx for ur help.
What is your extract fans m3/h rating?
I would recommend at least 202m3, although little less would be ok. Ideally more.
Add 10%-15% m3/h more when using carbon filter. (Due to reduce air flow)
Reduce for air cooled hood. (Temps will be lower in tent as most heat is removed)
Reduce for winter temps, increase for summer temps.
I would go for higher m3/h fan, you can always use a fan speed controller to reduce speed if need, and you can run on full speed when needed.
I use a 316m/h fan on slower setting, but now summer is starting I have set to full speed.