Mechanical filtration and vacuuming remove large bits of uneaten junk in a saltwater aquarium. However, one of the great advantages that marine aquariums have over freshwater aquariums is that there are all sorts of natural critters in the ocean that can be put to work to do a majority of the small-scale cleaning and maintenance for you. Reef-safe "sand sifters" are the category of animals that process the sandy substrate at all levels, consuming algae, detritus, and uneaten food without adversely affecting fish, corals or other invertebrates in your aquarium. Be careful to choose the right critters for this important job. Here is a look at eight very different animals and the different ways in which they comb through the sand in your tank.
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The tiger sand conch (Strombus sp.) is a popular one. Spending all of their time cleaning and aerating the sand bed, they might even disappear into the bottom for long periods of time (sometimes for months). Completely reef-safe, it will not even harm beneficial sand microfauna, nor will it seriously disturb the beneficial bacterial zones in the sand layers.
Even as they perform their valuable duty as scavengers and sand sifters, they are also amusing to watch as they dive in and out of the sediments. Adaptable, hardy and benevolent towards its tankmates, just a few conch will make a positive impact on the health and appearance of any aquarium substrate.
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Hermit crabs are great sand-stirring invertebrates. Reef-safe hermit crabs spend all of their time looking for and consuming algae and detritus. Smaller species of hermit crabs are preferred over the larger species, as they will not disturb the tank environment when they drag their large, heavy shell homes along the bottom and reef surface.
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The docile Goatfishes, especially the red goatfish, are the most charismatic of all of the sand sifters. They really dig in, shovel, and blow sand around as they fish for invertebrates like small worms. Goatfishes have beard-like appendages called "barbels," both long and short, on their lower lip used to taste the sand for sources of food. You may have to move some sand back where it came from as they act a little like a leaf blower!
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Sand sifting sea stars (starfish) are exceptionally reef-safe; they only provide benefits to your tank. Every marine tank should have one of these long-lived beautiful animals. Sand sifting sea stars generally come from one of two genera of the class Asteroidea (starfishes).
Astropecten polyacanthus are the most common, and they are excellent sand bed cleaners, but they can be too good! Some reef enthusiasts choose not to have them, as they can even strip the sand of the beneficial bacteria needed for biofiltration. For this reason, it is not wise to place them in a small aquarium or a new "clean" aquarium, where they will likely starve.Continue to 5 of 8 below.
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Segmented into five body parts just like their attractive cousins, the starfish, the "caterpillar-like" sea cucumbers are arguably the ugliest animals you can put in a saltwater aquarium. And yet a number of these species do an excellent job of cleaning the sand surface as they inch along at glacial speed. Sea cucumbers will not only consume detritus and uneaten food but also snails and other sand-dwelling critters, so keep an eye on them.
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Most marine crabs are well known for having voracious appetites, consuming detritus, uneaten food, and carrion in saltwater aquariums. Unfortunately, most crabs will eat just about anything else in your tank, including healthy corals, invertebrates, and fish.
However, there are a few reef-safe crabs that will not consume the "good" animals in your reef tank. Still, take caution when placing crabs. Even with the "safe" crab species, you will occasionally come across a rebel that does not leave corals or invertebrates alone.
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Gobies are among the most beautiful and entertaining fish found in saltwater aquariums. Some (not all) gobies process the sand substrate in an aquarium in search of algae and detritus. The sand sifting goby species literally chew the sand, removing the food particles. Then they either spit the sand out of their mouths or eject it out backward through their gills.
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Different snail species prefer different kinds of food: diatom films, plant-like algae, worms, and detritus. So knowing what your tank is prone to will help you choose the best snails.
Rock-dwelling snails spend all of their time on the rocks in a saltwater aquarium or even on the glass, avoiding sandy bottoms that are a hazard to them. These snails cannot extend their foot far enough from their shell to turn themselves over if they end up on their "backs."
But there are some great reef-safe sand sifting snails that can flip over when they need to, avoiding starvation and predation; these will happily consume the detritus and algae in your sandy substrate. The Nassarius snail even descends into the sand bed with only their snorkel sticking out. This behavior helps to keep the sand stirred.