Welcome. I'm using co2 in my current grow in a sealed room and at 1200ppm with a +or- band of 100 ppm I will go through a 50lb tank in two weeks ..but my room is around 960 cubic feet and these ladies are Thick and Healthy (I'm grateful for that ) . Now you say you are running it at 1400 ppm but then state you have the flow rate set to 3.. My advice is get a controller so you can actually see the concentration of co2 and set the sensor at the highest point of your plants, and make sure that at bare minimum everything from that point down is sealed on that tent as co2 is heavier than air and it will leak out any hole in the tent below that line. I agree the best thing would be to seal the room the tents are in .
