HAHA from Humidifiers to CO2... awesome...
How about, dehumidifying options for a small space 3x4x4 ft with VERY high humidity? I'd welcome unorthodox (i.e.: other than a dehumidifier) solutions, but also opinions on good small ones.
As to CO2... I'm sure it's been said before I just don't want to back track:
You need to use it in a sealed grow space, as in both you need a sealed grow space for it to be useful, and conversely you need to use it if you have a sealed grow space (see since 1991's post above).
If you are using a CO2 system, a regulator is pretty much necessary.
BE CAREFUL! If you're using it in a large space (Like a grow room) that you spend time in (like tending to plants) and you're levels are high... that is not safe for you. Also i you have it in a small space, let's say a bedroom closet, and it leaks that's not safe either.
There is a simple way to add some CO2 to either space: Home-brewing. Fermentation produces high quantities of CO2... definitely plenty to help your grow... depending on it's size and your brew size. May not reach the levels of a tank system, but effective, can be done easily and inexpensively, with the added bonus of getting you alcohol. Rising dough is another option.. if you like home made bread... though a little trickier (bread yeast is fast acting)