not sure how reputable this source is (it was linked from Bulk Reef Supply). Good read on carbon though, if you haven't already read it. In summery, don't use carbon 24/7 and don't run it passively and don't use too much carbon and don't flow too much through your reactor. In other words, pretty much everything I'm currently doing wrong with my carbon use
http://web.archive.org/web/200009180.../1/default.asp