I've got nearly a dozen AC 70's and the only thing I add is a second sponge along with the Biomax that comes with it, nothing needs to be changed.
I experimented with Purigen a few years ago with regards they claim it can lower nitrates, remove tannins, and keep water crystal clear but honestly it did nothing in my opinion that more water changes can't do. I'd save the money to purchase more Prime for weekly water changes, this will yield better growth and color with crystal clear water.