Well I hope you have luck with a phosban b/c i had mine for 2 months, it cracked and i upgraded. Many people have had success tho so maybe it was just me. Anyway yes you can run carbon and GFO
( the media for phosphate removal). But I would not recommended both in the same canister. They require different flow rates. Start out with the recommendation that will most likely be on the media container then go from there. I would ditch the HOB
filter as IMO
filters on saltwater reefs are junk and hogging space. Invest in another reactor for biopellets or carbon and get yourself a high quality skimmer. I dont have a sump and this is my equipment list. Reef Octo BH-2000 skimmer, Next Reef MR 1 reactor (phosphate), JBJ ATO with BRS 50ml per min pump, 2BRS 1.1ml pumps for 2-part, also I have vega LED
's, Jebao pumps and a Jäger Hearer. I have switched most of my equipment twice and think i got the best combination. Now I just have to add a Biopellet reactor and I'll be set.