By Robert Lashlee

• Turbo snails – These are very large snails and are great at algae grazing, but be careful because their size can topple live rock. Some people avoid them for this reason. If you have a large aquarium though, these snails can cover a lot of area and keep you from buying hundreds of smaller snails. Just make sure your live rock is secure. You also need to make sure there is enough for these snails to eat because they are so effective at eating algae that they can starve before enough algae grows back. For this reason, you should also not add these snails immediately after your tank cycles. Instead, wait several months for a food source to develop.
• Asterea snails – These are good snails for getting rid of brown and green algae from the walls of your tank, from your live rock, and from your substrate (they will not eat longer hair algae). They are also useful for smaller tanks because they do not grow larger than an inch. They do have problems, however, when they are flipped over as they cannot get back to their correct orientation and will die. If you see one on its back, you should flip it over.
• Trochus snails – Trochus snails are very similar to Astereas in terms of their algae eating, but they can rescue themselves when they are flipped over. They also stay small, making them a nice addition to smaller aquariums.
• Nerite snails – Again, this is a small snail (less than an inch) that is very good at eating algae off the tank walls. They will even come out of the water from time-to-time. They are also included in many hobbyists’ refugiums as they do great with marine plants.
• Nassarius snails – These are one of the most interesting snails you can add to your clean-up crew (even though you will not be seeing much of them) and they target an area of the tank not addressed by the snails listed above - in the sand bed. These snails actually bury themselves in the sand and are excellent at sifting and stirring the sand as they burrow through it. They have a long siphon tube that protrudes from their front and you can often see it sticking out of the sand if you look closely. They will also come out of the sand bed to eat (again, a neat thing to watch) and will feed on many forms of detritus that other snails ignore. They do require a deep sand bed (at least 4”) for their survival and should only be added after the tank matures for several months after the cycle. These snails are relentless eaters and are a must for agitating your sand bed.

• Red-legged Hermit Crab (also known as the Scarlet Reef Hermit Crab or the Red Reef Crab) – These crabs do an excellent job of scavenging and keeping algae under control (they will even eat hair algae which most snails avoid). They will also eat fish food. They stay small and are very hardy. Unlike most hermit crabs, they are generally peaceful towards others in the tank. They can sometimes attack snails although the Red Hermit Crab is much less likely to do this than the Blue-legged hermit. To mitigate this problem, toss some spare shells in the tank so they are not fighting the snails for theirs. As they grow and molt, they will look for new shells so it is important to offer these larger spares. They are considered reef safe.
• Blue-legged Hermit Crab – Another popular crab that will relentlessly eat just about anything in your aquarium (algae, scraps of food, etc.). They are reef safe (although some people do report they can kill specimens that are injured or dying), but have been known to be aggressive towards snails (although not to the point where you’ll be losing snails every day or anything. Usually the snails can fend them off). Adding spare shells of a variety of sizes to the tank will help reduce this aggression. Their bright blue legs are stunning and they are a great addition to a reef tank.
• Sally Lightfoot Crab – Again a relentless eater. It will scavenge around the tank looking for bits of food or detritus and pick at algae constantly. They are generally considered reef safe although the larger ones have been reported to eat injured or dead fish if they cannot find other food sources (you should, therefore, use caution). They also will crawl around on the corals a great deal, but this does not generally lead to problems. They get to be about 2-3” in size.
• Emerald Green Crab (also known as the Emerald Mithrax Crab) – This crab stays fairly small (1.5”) and is considered peaceful and reef safe. The only time they have been known to munch on corals or fish is if their food supply runs out (you can supplement their diet with dried seaweed, fish food, and meaty foods). If well fed, they get along perfectly well with other inhabitants. It is also well known for its ability to eat bubble algae, something very few reef safe species do. 

• Cleaner Shrimps – The most popular cleaner shrimps are the Pacific Cleaner Shrimp and the Scarlet Cleaner Shrimp (also known as the Red or Fire Shrimp). These shrimps do an excellent job of scavenging for leftover food, but they also pick parasites off of fish and are used to control saltwater ich.
• Coral Banded Shrimp – Again a very popular scavenger and a very beautiful shrimp in general. They are considered reef safe, but some have reported that they kill fish. However, most people disagree with these reports saying they are aggressive towards their territory and will chase fish away, but they will not actually kill a fish.
•  Peppermint Shrimp – Make sure you get a true Peppermint Shrimp and not the similar looking Camelback Shrimp because only the true Peppermint Shrimp is reef safe. These shrimp are excellent scavengers and are one of the best methods for controlling Aiptasia.
• Sand Sifting Starfish – These can reach sizes up to 12” so they should only be used in larger aquariums with deep sand beds. You also need to ensure there is an adequate food supply so they should only be added to established aquariums. They do an excellent job of sifting through the sand and turning it over. They also consume uneaten food and detritus.

• Asterea snails are usually kept at one per six or seven gallons due to their annoying habit of dying when they are flipped over.
• Trochus snails can be kept at as many as one per gallon.
• Nerite snails can also be kept at as many as one per gallon.
• Turbo snails should only be kept at one per every seven or eight gallons due to their size and extreme algae eating ability.
• Nassarius snails are generally kept at one per three gallons, but they depend more on the area of the substrate. If you have a tall tank then perhaps only keep one per five gallons.