Works best in a reactor.
Pros:
Removes organics and pollutants
Clears water
Cons:
Can deplete trace elements
Removes the yellow from your water (you can't see it but it's there) and abruptly increases the light to corals
If you don't rinse it well enough. the dust can play havoc on tangs
It's really only effective for about 3 days but that's plenty. I run it occasionally.