Boris wrote:

I've seen these at Big Al's Aquarium Services. Has anyone ever used one.
Here's a link:

http://www.belowwater.com/products/carbo-plus/

While the start-up cost is low, it seems that replacing the carbon block
every 6 to 8 weeks is expensive.

The start-up cost is not that low, and with a new block every 6-8 weeks, you
pass the cost of pressurized CO2 within 3-4 months. Seems like a waste to
me.