Geo 618 here, love it, no complaints. I did add a second media chamber for more Ca media and Magnesium media to help use up any left over CO2, before going back into the sump. I would recommend using a controller vs. a monitor for controlling the reactor, I don't like using just a bubble count method(it can change over time). Good luck, I'm so happy I don't have to remember to dose two-part every night, one of the best things I have added to the tank.
Matt