Just put a full canister of CO2 in the room, and let it leak out with a hose making the gas come out in the middle of the four girls. This helped give a boost to growth last time. I'm still on a 24/0 grow light cycle, seeing as they're autoflowers, and that's what everyone said to do. I might switch to a 20/4 in the morning, though. Growth seems to be stunted.