The bigger ones are in flower? You can clone from plants in flower, it is just more difficult, takes longer, and has a greater mortality rate, than from plants in veg. I recommend doing it earlier in flower as opposed to later.

Co2 is not the only reason for circulating air over the canopy. What trick does the tablet seem to be doing? Keeping mold away or helping the stems to grow strong so they can hold the weight of buds? Or am I not understanding something? (It's been known to happen.)