That co2 cylindar runs out really fast regardless. The system is not a good one, yes, I own it.
When the current cylinder runs out, probably happened today, I won't buy anymore. I'm working on setting up a real pressurized system. The way it's going, it'll end up costing me $150 or so dollars with enough co2 in the tank to last me a year. Using the 20g cartridges, I'm looking at $200 per year in co2 every year. The numbers don't add up.
Now, mine came with my fluval flora, but I would never recommend anybody buy this setup. Although, it's an inexpensive way to get introduced to co2. I suppose it's like a gateway drug.