I suggest that you find a local welding supply store near by. Check to see if they sell used tanks and what are their prices. Unless you want to have one of those nice looking aluminum tank, you will be swapping tanks each time you go in for refill. Most place won't have too many 5lbs so you may not get swap each time. They will tell you that most aquarium users uses 10lbs tank. Don't forget to ask if they seel permaseal there. If not, you may want to order one when you are ordering stuff for your co2 setup.