Can I run GFO and activated carbon together in a reef tank?

Yes, you can run GFO and activated carbon together in a reef tank, and many reef keepers do this safely. GFO helps lower phosphate, while activated carbon removes dissolved organics and improves clarity. Start slowly so nutrients do not swing too quickly. Use roughly half of the recommended amount for both media during the first week. Rinse each media well before adding it to a reactor or media bag. Keep flow moderate; GFO should move gently, not tumble hard. Test phosphate every few days at first, then weekly once stable. Replace carbon every two to four weeks, and replace GFO when phosphate begins to rise instead of blindly swapping on a fixed date. If corals retract or pale suddenly, reduce media and make changes more gradually. Track your results over time and adjust based on tests rather than guesswork.