Best way to run AC110 in FOWLR 75 gallon.

[ReefLover]

Ok so here goes a question since i have searched all over and have yet to find an answer. I am running an AC110 in my 75 gallon FOWLR along with the Reef Octopus BH 2000 Skimmer which I LOVE. I have about 40 Pounds of Live rock and its Bare bottom, i have a 3 inch blue face Angel and a small tomato clown, nothing else is in this tank. It has been running for over 6 weeks. My question is regarding the AC110, i am running it with the carbon it came with, along with the noodles it came with, and the sponge it came with. I still have Nitrite and Nitrate level problems. Now the fish have been fine and are eating fine and they have been super healthy, i am doing a 20 gallon water change every other week and my levels are still NOT at zero where i would like them. I suspect that i may be running the AC110 in an incorrect way for a saltwater set up. Perhaps the media i have in it may NOT be what should be in it. Also what is the best way to do a safe bi weekly cleaning to this filter WITHOUT killing the needed bacteria already in there? Any and all help will be appreciated. I keep African cichlids, i have a 90 gallon and a 180 with African cichlids, my 75 is so far my only saltwater FOWLR tank.