I've seen those CO2 reactors many times but I've never understood quite how they work. it looks like there's an air hose from the CO2 bottle running into the gravel vac and a pump hooked up to the top of the gravel vac with a piece of sponge at the bottom, but how does all that work and what does it do?
edit: please forgive me for not saying before but I love your tank as well very nice.