The Hagen Nutrafin CO2 system. I chose this because I did not want to spend too much on pressurized CO2 system and did not want to mess about with home-made system, so this kit has all I need to get started for my plated tank at a reasonable price. All you need to do is add sugar, one packet of activator (it is actually yeast) and a packet of stabilizer (Sodium bicarbonate/baking soda) and warm water to start the culture. The manufacturer claims that each culture will last about a month. The first bubble started after about one day. At first, the bubbles got stuck on the ladder but after a few days when slime coats started to line the ladder, the bubbles will run smoothly and gradually up the ladder. As it travels up the ladder it will become smaller and smaller due to the absorbtion into the water.