So, your tank has finally cycled and you thought you were through the rough stuff and could sit back and enjoy your new hobby. Suddenly there this brown stuff starting to grow on everything in the tank. You can read all of the books and all of the articles about Brown Algae or Golden Diatom on exactly what it is (it's not really an algae, it's a diatom) why it exists (because it can) and all of the longwinded explanations on how to get rid of it, but the bottom line is that you have a Brown Algae outbreak and it's not going away quickly on its own.

Brown Algae needs light (your tank lights are perfect) and food (nitrates and silicates) to survive. The cure for Brown Algae is the same as the prevention: Starve it into oblivion.

Nitrates can be introduced into an aquarium not only as the end product of the Nitrogen Cycling Process (ammonia/nitrite/nitrate), but also via some brands of commercial sea salts and tap water. You can scroll down to see methods for reducing nitrates.

The silicates the Brown Algae requires can enter your tank through several avenues: Commercial sea salts, tap water used for top offs and make up and the substrate you may have on the bottom of your tank.

If you did absolutely nothing to your tank, the Brown Algae would eventually consume the silicates present and die of starvation. Since you can't do absolutely nothing to your tank, the source of the silicates must be identified and eliminated, in order to get rid of the present brown algae bloom and prevent future outbreaks.
 

• Check the source of any builders sand, play sand or other substrate materials in your tank which did not come from the ocean. There is a possibility that they may contain silicates which are leaching into your tank water.
• Use only RO or RO/DI water whether you purchase RO/DI water from a commercial source or buy a RO/DI unit for yourself..
• Check to see if your commercial sea salts contain high levels of nitrates. If the salt mixture contains unacceptable nitrates, consider changing mixtures.

Removing the silicates alone from your tank will eliminate the Brown Algae problem. But, as long as you are getting your tank in order, you might as well get used to dealing with nitrates. This would be a good time for you to establish a good tank maintenance routine which includes keeping nitrate levels at a minimum, especially if you plan to have invertebrates and/or a reef tank, which do not tolerate high levels.

Nitrates will always be something to contend with in your tank. For fast, immediate reduction, you can do a water change, using the Instant Nitrate Reduction method.  This will reduce your nitrates at the fastest rate, using the least amount of time and water. This will also get your nitrates down to a workable (10 mg/L area) level but it is only a Bandaid and does nothing to remove the source of the nitrates. Siphon out as much of the Brown Algae as possible. You will probably find that you will have to use several other methods (many of which are part of a good aquarium maintenance routine to keep your nitrates in check.
 

• Use only RO or RO/DI water or purchase RO/DI water from a commercial source. (Recommended)
• Purchase and use Mangrove Plants in your tank or sump. (Recommended)
• Check to see if your commercial sea salts contain high levels of ammonia/nitrogen.
• Purchase and use a good  "nitrate sponge".
• Do not overfeed your tank.
• Siphon uneaten food and other loose material (detritus) from the substrate.
• Perform periodic water changes.

By reducing the nitrate and silicate levels, your tank will soon be healthy and free of the Brown Algae. Many of your tank occupants (corals and other invertebrates) will also benefit from the reduced levels.