There are several (from the Middle English word meaning "many") species of blennies that principally consume algae... A cursory view of the ones that have been listed as members of the genus Salarias on fishbase.org will show a grand number of 159... but for our purposes here, we'll discuss the two genera, three species of comb-tooth blennies (family Blenniidae) that are specifically sold as "Lawnmower or algae blennies" largely in the trade.
Mostly employed as erstwhile nuisance algal cleaner-uppers, the genera Atrosalarias and Salarias blennies are well-deserving of their prodigious green-eating capacity, and can make good tankmate fish additions, given a few caveats. One, that they are placed in well-established settings (with sufficient edible algal growth), of adequate volume (most die from starvation... indirectly from being placed in too small quarters... Thirdly, that they not be housed with overly-aggressive nor habitat-sharing organisms (they're feisty to put it mildly, and don't like sharing the bottom algal patch they call home).
Species on Parade:
Genus Atrosalarias: Monotypic (one species).
Salarias, Lawnmower Blennies. Much-loved by aquarists as algae groomers. Seven nominal species, two of which show up in the trade/hobby regularly.
As with most territorial fish species, these blennies are best purchased small, and placed near last to provide your best chance at establishing a livable pecking order. How small is small? Two inches for Atrosalarias, two and a half to three maximum for Salarias spp.
Take care to not purchase a "too-thin" specimen that has been on hand and starved for too long, but on the other hand, don't be too anxious to acquire a just arrived individual either. Ones that are going to "die mysteriously" do so most often in the first few days of arrival.
Torn fins are not indicative of a doomed specimen, as these blenniids are rapid healers. Cloudy eyes, missing scales, sores on the body would disqualify a purchase however. Do watch/observe carefully for active, inquisitive behavior, hallmarks of a winning specimen.
Expanding on the above environmental conditions, the size, maturity of a given system intended for these fishes is paramount in determining your successfully keeping them. Even starting with the smaller Atrosalarias fuscus or a very small specimen, a minimum of an undercrowded sixty gallons with this or more pounds of matured live rock is suggested. As you will find, these species claim an easy equivalent of bottom space as their own as this... With a hundred gallons per for a full size (five inch or so) Salarias fasciatus, being about right.
These are by nature territorial fishes, that will drive out other animals, including of their own kind, from their algal patch area... how to put this.... with extreme prejudice. Algae eating tangs like Ctenochaetus, many Zebrasoma, small Rabbitfishes/Spinefoots... sessile invertebrates that make their living rasping the bottom, may have a tough go at living in the same small space as these blennies. If you would like to try mixing them, do place the blenny last.
Other blennies/oids and families of fishes are generally ignored, or just chased for the halibut by algae blennies, as long as their not filamentous algae eaters.
These fishes are algae eaters par excellence, but not all algae. The vast majority of their diet in the wild is made up of filamentous green algae species... a bit of red (Rhodohphyte) and brown (Phaeophyte)... they don't eat all types (e.g. not "bubble", Family Valoniaceae), species, and almost entirely ignore Cyanophytes, aka Blue Green Algae... that despite its common name occurs in all colors, and shapes... blue, black, green, red... almost always slimy to the touch. Most types of prepared, meaty foods are ignored, or if taken, with not enough enthusiasm to support these fishes.
Often, with aging of a captive system, there will be a shift in the make-up of micro- and macro-life that predominates... and a valuable lesson for observant aquarists in the loss of fodder for such grazers as these blennies. The very best gauge of such incurring change is a thinning of said fishes... first in the gut area, but spreading to the upper flank musculature. Such changes can occur quickly, in days, and supplemented foods must be made available to prevent loss. Of most use are prepared foods in the form of sinking wafers and pellets that are largely algae-based. Various of these have been shown to be accepted with gusto.
Alternatively, cultured macro-algae, dried people-intended algae like Nori, Kombu... can be tried, and with familiarity are generally accepted as well. For true "die-hards" hoping to entrain natural behavior, "algae rocks" can be cultured elsewhere (as in a lighted sump) and rotated into the main system periodically.
Diseases/Prevention & Cure:
Algae blennies are the epitome of industriousness... only taking time to rest during daylight hours between surveying their domain and nipping at loose bits of filamentous algae. One that is too sedentary is trouble, and a wake-up call to check your water quality and/or gear.
These blenniids are subject to the usual reef fish scourges, and amenable to the usual treatments, though they shy on the narrow margin in actual treatment regimens and chemical concentrations. Hence you should take care to know the actual gallonage of the water being treated, and use test kits... often and regularly if/when dosing them.
Most transferable ailments can be excluded by a two week quarantine period prior to placing them in your main system, with a suggested Methylene Blue and pH-adjusted freshwater dip enroute.
Thus my pertinent notes re the aquarium use of these two genera's members... Comical, tough and only-to-a-degree (compared with the Blennies of the genus Ophioblennius: ten described species, which can be territorial terrors.
Atrosalarias and Salarias blennies can be put to good use in established marine systems of good size, with filamentous green algae in abundance (or supplementary feeding) and a dearth of tankmates with similar feeding strategy.
Baensch, Hans A. & Helmut Debelius. 1994. Marine Atlas, v. 1. MERGUS, Germany.
Burgess, Warren E., Herbert R. Axelrod & Ray E. Hunziker. 1990. Atlas of Aquarium Fishes, v. 1. Marines. T.F.H. Publ. NJ.
Dakin, Nick. 1992. The Book of the Marine Aquarium. Tetra Press.
Nelson, Joseph S. 1994. Fishes of the World, 3d ed. John Wiley & Sons, NY.
Thresher, R.E. 1984. Reproduction in Reef Fishes. T.F.H. Publ., NJ.