Maintenance on a Reef fish tank is the determining factor in whether or not you will have a thriving aquarium, or an algae infested swamp. If you do not keep up with certain basic things, your aquarium will fail.
To start, one of the most important things you can can do to keep your reef and it inhabitants healthy, are water changes. Keeping up on regular water changes will help control certain chemical levels as well as reduce the amount of waste that accumulates in your fish tank. One of the more important functions of a water change is the removal of nitrates, which is a chemical harmful to fish and also attributes to the growth of algae, from the aquarium. As a rule of thumb, the percentage water changed is equal to the percent of nitrate removed from the tank.
It is important to remember that you should not start your water changes on a newly set up tank until after the tank has fully cycled. For more information on cycling, please read the Cycling Your New Tank article.
For Information on how to do a proper water change, please read How to Do A Reef Water Change. Doing a water change can be stressful for your marine inhabitants so it is imperative that you do it correctly.