Okay from the other side of the park - I run two magnum 350 cannisters of carbon 24/7. Every 2 weeks I cange out the carbon in one of them. I change 25 gallons every month, top off weekly, and whenever something new is added to system the drip acclimated water is replaced with new saltwater. The tank is a 210 with 40 gallon sump system. Weekly I dose Reefcomplete, Super dKH buffer, and Turbo calcium, and 1 cap of iodine.
Inhabitants are Zo's (12 diferent colonies), paly's, 10 different musshroom colonies, pulsing Xenia, green starburst, trachyphelia's, montipora's, gonipora, hemmer, torch, toadstool leather, candy cane, trumpets, sun corals, pipe organ, acropa, clams, feather dusters, and around 200 inverts (snails, hermits, shrinps, etc). Weekly I notice a drop of 30 - 40 points in calcium, 40 - 60 points in Alk (measured in ppm CaCO3), and .01 - .02 drop in iodine levels.
I went 4 weeks without carbon and consumption rates remained the same, but coral polyp extension was way down. I am a believer in carbon!
Denny