[northtexasfossilguy]

You ought to get a 20lb tank if you have a larger aquarium while you are at it. Use the soda machine kind, they are cheap as can be. Like $60 I think. They charge a flat rate everywhere.

If you find that your 5lb tank is small and runs out quite often, then its a good idea to get a bigger one. My 20lb has 1500 psi and has dropped almost imperceptibly since I got it filled last. I think your rate was about right what you paid, because its likely a flat rate no matter the canister size, not sure? That's what I paid for four times the gas, though.