I run carbon (black diamond) 24/7 in my reef and change about every 2 weeks. I prefer to force flow though it via a canister filter (no other media in it) for best results. If you have lighing in your sump you should consider some type of macro algae such as cheato, which will help eliminate some of your micro bubbles once it gets growing. Although, if you sump is baffled correctly you really shouldn't have an issue with micro bubbles.