That is a difficult question, and one which I cannot directly answer because most algae eaters have a type they are most fond of and many of these creatures may well ignore other types. What needs to be done is consider the algae that is causing a problem and hopefully choose a creature to eat it.
The first creatures to consider are fish. Many fish are herbivorous and continue this habit in the aquarium. With some fish algae is an essential, and a lack of it could cause health problems. The numbers of herbivorous fish are too high to go through one by one, but two in particular will be very generally mentioned, using their common group name.
The first fish are the so called rabbit fishes (a well known one among these is the yellow â€˜Foxface,â€˜ Lo vulpinus). These fish will eat algae provided by the aquarist along with normal food. They will also often eat [tag-tec]hair algae[/tag-tec] within their limits (a lone rabbit fish cannot be expected to control a serious problem). A point to bear in mind with this group of fish is that the dorsal spines are poisonous and the aquarist should exercise care.
Another well known group of fish are the surgeons or tangs (a well known one is the powder blue, Acanthurus leucosternon). This group of fish are [tag-ice]algae grazers[/tag-ice] and often travel in large shoals on the wild reef. This group will eat algae and other food provided by the aquarist, and if there isnâ€™t any algae in the aquarium some must be provided preferably daily. It is possible that they will attack hair algae.
The problem with fish is that they are â€™largeâ€™, and unless a suitably large aquarium is in use they are not in sufficient number to be effective. Small nano aquariums are too small for surgeons etc but of course they could still suffer from algae problems.
The solution that is employed by the majority of aquarists for many different sized aquariums is the introduction of [tag-self]aquarium snails[/tag-self]. These snails are an interesting and very useful addition as they consume algae. Some will also consume detritus. As far as I know, there isnâ€™t a snail type that is â€˜all singing all dancing,â€™ but they can be used for different purposes, all toward the control of algae.
The snail possibly best known is the Turbo Snail. These snails however will not usually eat hair algae but will graze small surface algae, and they do this very well. Further to the mentioned snail is the so-called Super Turbo. This one will eat hair algae and many other types, and they will do it with more gusto, hence the name (I assume).
Trochus snails are another that will eat hair algae, and also small surface algae and diatoms (brown algae caused by silicon). The brown algae that sometimes appears will often disappear of its own accord when the silicon supply exhausts.
If there is a sand bed in the aquarium then the Cerith snail is of use. It buries itself in the sand and helps to keep it healthy by aiding in compaction prevention. As far as algae is concerned, they come to the surface of the sand and feed on any film of algae that is there, and may well move to the glass and feed from that too before returning to the sand.
This is not by any means an exhaustive list of algae eating creatures suitable for the seawater aquarium. Hopefully it gives a direction for consideration and research should algae become a problem.
Of course, the aquarist should consider why there is an algae problem and take measures to correct the cause. For instance, are phosphate and nitrate measurements too high? Algae eaters are great assistants but have limits.
Having a few snails in a marine aquarium is usually fine, with quality live rock there is normally enough food for them to eat. However, as with other forms of livestock, they can be overstocked. It is of little use putting a high number of any particular type of snail into the aquarium – it is probable that the food source will be exhausted and the snails, or some of them, will die. The idea is to strike a balance where the aquarist is happy with the controlled algae level and the snails are healthy and happily munching away. So consider which algae(s) present the problem and select a snail or snails to suit. Then purchase three or four of each type needed. Introduce them to the aquarium and observe the impact on the algae. It can be judged at what speed the algae is consumed against its growth. Then an additional number of snails can be obtained and further observation undertaken.
In the home marine aquarium the aquarist will never achieve the diversity and balance found on the wild reef. However, with patience, research and observation a controlled situation can be achieved.