So i have a 75 gallon freshwater fish tank and i just started using a red sea co2 pro kit and i am thinking about larger tanks. I am not sure as to where i can get the bigger ones filled. Also how long do the tanks usually last? at one bubble per second? The one i have now is 20 oz, also if it is hard to fill the larger tanks like 10 gallons is there a way to put two smaller tanks n one unit so it will last longer?