If you want to have a healthy saltwater aquarium that is algae free, you will have to take steps to remove the nitrates, phosphates and other nutrients that contribute to algae growth in your tank. People have come up with a variety of ways to keep nitrates down, from dosing sugar to operating denitrating coils. Our solution is to use macro algae and mangroves along with traditional methods of filtration. In time, a macro/mangrove planted tank or sump can remove nitrates, phosphates, and other harmful chemicals from your water.
The ideal refugium/sump utilizes both mangroves and macro algae to achieve the desired results. The reason is because mangroves grow up and out of the aquarium, and require little tank volume to grow. Below and among the mangroves there will remain ample room for macroalgae to be grown between the roots of the small trees. This growth helps stabilize the roots of the trees, and give the macro something to cling too. This win-win situation is common in nature.
When it comes to filtering nitrates and phosphates out of an aquarium, not many macros are better at achieving results than caulerpa. However, because certain caulerpa species have a greater tendency to go sexual and release nutrients back into the tank; the novice aquarist should take pre-caution before introducing it to their tank. In order to reduce this risk, make sure to regularly prune the algae so it does not starve, and to keep it well lit. The risk of caulerpa going sexual can be reduced by growing it in a sump that receives light 24 hours a day. Other species of macroalgae won't benefit from the constant light, and will do fine with a 12 hour photocycle. More information on caulerpa can be found in our growing guides , and our general macro algae care guide .
The most popular filtering algae species in the hobby are members of the Chaetomorpha family. Chaetomorpha linum and Chaetomorpha crassa are the two species generally referred to as "chaeto". While they will not remove nutrients as effectively as caulerpa, it presents a very low risk of going sexual and harming your tank. It still does an excellent job at filtering and a better job than caulerpa when it comes to providing a home for microfauna such as copepods. It also grows well within the root structure of mangroves, and is easy to harvest. Other important filtering algaes include Ulva and Gracilaria - which can be fed to herbivorous fish, keeping your tank self sustaining - to some degree at least.
By adding macro algae and mangroves to your reef system, (either by placing it directly in the display tank or in the refugium), you are bringing your own reef closer to those found in the wild. In nature, every coral reef that benefits from the filtering properties of macroalgae. Some reefs are mixed, and include coral and macroalgae living side by side, this is similar to placing macro algae directly in your display reef tank. Other systems have extensive macro algae fields in the "back reef", and have their nutrients washed out to mangrove islands before the water returns. Such reefs are found extensively in the Florida Keys.This is similar to having a system where the refugium/sump is filled with macro algae and mangroves and the display tank is coral dominated.