How long would this C02 last in my tank?

[Pyramid_Party]

I was thinking about buying this kit. How long would this amount of C02 last in a 29 gallon? http://cgi.ebay.com/Aquarium-CO2-sy...503?pt=LH_DefaultDomain_0&hash=item3cb22ffa67


Also, it says the cylinders are non refillable. I see they sell cartridges. Is it possible I could buy my own refillable cylinder later and use it with this kit? Thanks

 

[123456]

Looks like a pretty cool kit for 30 bucks.

I don't think it'd last that long in a 29g though.

The cartridge looks like the ones you can get at Fred Meyer or sporting goods stores where they sell CO2 pellet guns.