Rack\Bin Ventilation Question

I've recently built my first rack, using Melamine, 9 shelves, 41Qt tubs, and 6" heat tape on each shelf. Instead of using open tops, I've decided I'd prefer to keep the lids on the bins, since they snap on securely, and I don't want a hungry (or nervous) BP to bite me as soon as I slide the bin out. I originally put several air holes (~20) in this sides of each bin with a soldering iron, but I noticed I was getting condensation on the front (cool) sides. I doubled the number of holes, and added plenty of holes to the lids as well. The extra holes, in combination with a fan circulating the ambient air in the room has fixed my condensation problem, and I'm happy with the temps in the back\hot side, and in the front\cool sides. All the snakes are eating, shedding, and defecating normally. Nobody seems stressed, and everyone seems happy and healthy...but...I still have a lingering concern in the back of my head...

How can I tell if my bins provide enough fresh air? Is there a way to tell if there's enough fresh air, and no buildup of CO2?

Thanks in advance!

If you have that many holes, and the condensation is cleared up, I would say you have PLENTY of ventilation.

I'm curious about this as well. In general, how does one know that a tank or tub has enough airflow? Are there general signs to look out for that indicate insufficient ventilation?