I've got an old downflow Precision Marine and an Effluent chamber. Since its downflow I have to use course media in the main reactor to prevent frequent plugging but I am able to use fine in the Effluent chamber. Like the others I've got a pH probe installed in the top allowing me to control it easily with my Apex. I've been doing it this way since 2006 with no regrets. A 20lbs cylinder of CO2 lasts me about two years, I top off the reactors and calibrate the probes every 4 months or so and give the whole thing a good cleaning about once a year. Occasionally I have to turn up the flow but I haven't added calcium chloride in about 2 years or baking soda in nearly a year.
A Guide to Using Calcium Reactors
http://www.reefkeeping.com/issues/2002-05/sh/feature/