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With tiny mouths, snails move about your tank at a methodical pace, cleaning up junk that dirties your water, such as dead plant matter and leftover food. Some snails put the kibosh on algae, too. Although snails are effective at cleaning your tank, they resemble recycling plants more than garbage dumps -- after all, much of the nastiness they consume comes out the other end, in the end.
When algae foul up your beautiful plants, discolor your tank's walls and generally make your aquarium appear unflattering, some types of snails come to the rescue. The slow-moving creatures eat the greenish and brownish clumps that pop up inside your tank, leaving it looking nice and clean. Snails as a whole have a reputation for consuming lots of algae, but only certain species chow down on the organisms. Nerite snails are by far the most effective freshwater algae-eating snails. Apple and mystery snails occasionally pick at algae, but don't expect them to serve as your primary cleaning crew. Pond snails and ramshorn snails eat algae, but they can breed incredibly fast and overrun your tank. On the saltwater side, common algae-eaters include nerite, turbo and margarita snails. Nassarius snails are also common in saltwater tanks, but they're not big algae-eaters. Know that nerite snails will breed in saltwater but not in freshwater.
When you drop a pinch of fish food into your tank, your fish probably eat a good chunk of it, but some inevitably falls to the bottom. While some fish will pick at the food that lies on top of the substrate, they don't hold a candle to snails. The shelled invertebrates comb through the substrate, picking up and chowing down on leftovers. By doing so, they not only clean your substrate, they also help prevent food from decaying and producing ammonia.
Most aquatic snails are omnivores. That bodes well for your tank if you have live plants, because small pieces of dead plant matter often sink to the bottom of your tank. Like food, decaying plant matter produces ammonia. In most cases, snails will pick at the dead plant matter and leave live plants alone. Aquatic Community explains that the majority of snails aren't fans of certain poisons that live plants typically produce.
True Cleaning Value
A snail's penchant for cleaning tanks is a double-edged sword. On one hand, they remove decaying matter that accumulates, and some eliminate algae, but snails contribute waste as well. They're not removing much more than they're putting back into your tank. In the case of invasive snails, population explosions are so likely to occur that the snails may contribute more waste than they remove. FishChannel.com notes that "snails can become a major part of your bioload." As long as you don't overstock your tank or add invasive snails, you're unlikely to encounter problems, but be aware that snails aren't garbage trucks that take their loads to unseen dumps.
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