I just constructed this reactor, but I'm confused a bit. On the diagram a few pages back that micaa wrote, the input from the pump is clearly going into the input "in" on the reactor. The red button is closest to the input of the reactor so the Co2 comes through the pipe before it.
Does it make a huge difference what way the water flows through the thing?
EDIT: Upon closer examination of the reactor, the IN pipes directly to the top of the reactor. The OUT sucks water from the bottom of the reactor via the tube. This is how it's setup in my current min max reactor.