Depends what you have in there. If you have mainly soft corals and a good amount of fish you can get away with just water changes and no additives. Phospage removers can be useful, but there are no nitrate removes.
Most soft corals and LPS can just be fed Frozen food like your fish.
IF you have SPS Corals, which are hard corals like acropora, you will have to monitor and maintain calcium, magnesium and alkalinity, but this is very advanced. :)