Algae is a common problem among saltwater tanks. Many fish eat it, but it usually grows back too quickly for them to keep it under control. True algae needs light and nutrients to grow; by controlling it’s needs we can eliminate it.
The first need is light. If one has a reef tank, then cutting down on the amount of light the tank receives is not a practical option. However, it has been shown that by turning the lights off for an hour in the daytime, it reduces algae’s growth much more so than one would think. Scientists are not sure why--as you think the algae would lose just that one hour’s growth, but that’s not so. It actually loses a alot more growth than this. My theory is that it’s like a rolling stone: once it starts it’s growing for the day it will keep on and on until night; yet if stopped, it takes a while to get "organized and rolling again." Therefore this "light siesta," as some call it, can be one tool you can use to help fight algae.
There are many fish that eat algae. Among these, the Tangs cannot be beat. Some are known to prefer to eat only certain kinds of algae (we have heard Achilles’ Tangs love Red cyanobacteria) while others will eat almost any kind of algae (The Kole Tang is known for this). I have personally noticed though, that my Black Domino Damsel ate Green Algae like no other fish I have ever had--at an incredible rate for its size at the time, however this is only recommended for an aggressive fish only tank---as this fish is a lunatic in it’s aggression! It is reef safe though, but keeping fish like green chromis with it is asking for trouble, and I even saw mine chase my Yellow Tang around! So there are other fish that will eat algae, but the Tangs are usually the fish of choice. Some inverts may be considered as well, depending upon what kind of algae one has. The Black Domino Three Spot Damsel is a great canadite for green algae cleanup, but ONLY if you have a very aggressive tank setup!
Algae loves two nutrients in particular, Phosphate and Nitrate. Nitrate can be easily gotten rid of through water changes, while Phosphate is found in low quality salt mixes and chemicals and foods even, but mainly--in your tap water. There are Phosphate sponges, but most things like this are only a temporary cure. Reverse Osmosis devices are known to be good for eliminating much of the causes of algae, and other pests like diatoms (also called brown algae mats-- when alive they feed off of silicates). Good water changes and herbivore fish, along with maybe a "light siesta" and, if needed--a reverse osmosis device--seem to be some of the main ways to control algae so far.
Another way it to introduce another form of algae to take the place of a pesty form. The most practical example of this now-days is purple algae. This will take away some of the nutrients and space that the pesty form of algae needs to grow, and purple algae is very pretty. It can be found on almost all live rock of course. Be sure to add Calcium to the water to make it grow. A note: one thing one does NOT want to add to the water in a modern day saltwater tank is Iron, as it will cause algae to grow so quick it will just stun you.
Some inverts can help alot with algae. Little Blue legged crabs are good at eating various things, including brown algae. "Paguriste Cadenati, Clibanarius tricolor, and Calcinus Tibicen are good species to try" (quote from March 1999 Issue of Practical Fish Keeping Magazine). Shrimps will help sometimes as well. Various Starfish can be of help IF you get the right species and IF they are good quality stock, to scavenge the gravel bed and lower the amount of decaying matter that algae indirectly feeds off of. Sea Urchins may help as well, "but can be hazardous to some tanks because large ones can knock over corals and rocks, and may eat good purple algae as well." (PFM March) Sea Apples are to be advoided. Algae scrubber systems make a huge competitor for algae obviously, however we cannot recommend them due to the reasons discussed on our equipment pages.
It is very hard to find fish and inverts that will eat hair algae, so that may not be a viable option for this type. Another note: Various things will grow and then recede in the first 3 months of the tank being setup, therefore waiting a month or so before taking measures may be wise--as it may just disappear on its own. On the other hand, if the tank has been setup for awhile, delaying the measures you want to take may cause it to get even more out of hand. With good tank maintence and alot of patience, the problem should quickly vanish.