Planted Tank Guru
Join Date: Jul 2008
Location: East Lansing, MI, USA
The link to eBay is for a very small CO2 kit designed for a nano tank. The cartridges are not refillable. You may get a month out of each. Copperhead CO2 cartridges are expensive too, after a while. There isn't much in each cartridge and they too, aren't refillable. If you want irregularities lets talk timing of tiny cartridges.
You can smooth out a DIY yeast setup by using two bottles connected to a T. Swap one each week. Be sure to use a check valve on each.
That said, I've got to repeat what most will tell you, because we've been there and done that already. Standard off the shelf pressurized CO2 is really easier in the long run. It is also cheaper if you skip all the mis-steps on the way. A lot sooner if you ever spill a working yeast bottle on a significant others rug.
And, like many here, I'll say contact one of the sponsors of this forum and have them help you out. I happened to luck out and get a demo unit Orlando offered. That and a local cylinder deal got me a functional system with solenoid for about $150.