Some Carbon use/light intensity observations for ya.

[Acro]

Brad, Yeah I have noticed yellowing in the past when I do not use the carbon. I did have a refugium with caulerpa in it at the time though. My point was more do to the fact that the corals seemed to be reacting to the increase in light from the polishing of the water via carbon. If one used carbon more frequently the water would stay cleaner and the once a month shock would less likely happen. If his water is yellowing before the monthly change then to me he needs to change in more often or try running more at once. Just as an example: I always try to go to the washroom before I start going. If I happen to be a little late it's harder to clean up after then If I took care of it in time Sorry for my poor attempt at humor.