Some Carbon use/light intensity observations for ya.

[Aquattro]

Jon, I do run a refugium, but it has no algae in it if that's what you meant. And it is a recent addition. I just never found carbon to do anything, however I use it just in case! I'm sure it does a lot, I just don't see it.
Now that I think of it, I do have a 5g tank running that is turning quiteyellow. It has 1 rock and 1 acro in it, so I guess a SPS tank can turn yellow.
Jamie, do you notice a yellowing of your water?