i use dry ice enrichment and it works great
every night i break a chunk off a 5lb brick of dry ice and let it set on the soil and turn all my fans off and just let it sink in.
i reccomend you have a ventilated light fixture so that the stale c02 can be pulled out of the room cause if you have your fans all it just blows it all away and doesnt give it time to set into the plant or anything