Hey Included !

I miss overgrow too, but that isnt a reason to not overgrow again !

Sounds like hell your setup, but your space isnt very large as i can see.
Your Ventilation doesnt sound like overkill, you cant have enough ventilation when growing in a box. What you did miss to mention is your lightning power. How much watt is that bulb ?
Whats the temperature inside the box, and do u run your ventilation system allways on 100 % ?

About the CO2:
My CO2 systenm is incoming (growing in a box too), and i am wondering about the same question. The heat build up is large when you're using a total of 1000W in a box of 2m2. And my Outtake Vent is way to big to run it when injecting CO2 (~300 cfm).
Guess we have to find out self because there arent much information about this since overgrow went down.
On the other side i think its maybe overkill to use CO2 in a such small are like yours...

On the plants: They are looking good, hope u have fun !

Es gruessli

Herbarium