I used carbon religously for many years until I figured out that the organic contaminants being adsorbed by the carbon are metabolized by the nitrogen cycle bacteria as a carbon source. Also, if you're adding blackwater amendments, the carbon will remove them. Finally, there is emerging data which suggests that there is a correlation between carbon use and "hole-in-the-head" disease. Oh yeah...and it takes up space that I want to devote to biomedia.