How do I deal with aquarium snails?


Aquarium snails are considered a pest by some and a pal by others. Spotting snails in your aquarium may not cause any issue at first, but that novelty may quickly wears off and disrupt the eco-system - and when the numbers get out of hand, you’ll need to intervene.

What’s a nuisance snail?

Aquatic snails can be broadly placed into two camps: nuisance and ornamental. Ornamental snails, such as rabbit snails or zebra nerites, are usually large, attractive species that are purchased as a visual centrepiece. They are often slow to reproduce in aquaria.

By contrast, nuisance snails tend to comprise of either tadpole snails (Physella acuta), Malaysian trumpet snails (Melanoides tuberculata), or occasionally ramshorn snails (Planorbaris and Planorbella). These snails are smaller, less attractive, and can breed prodigiously, to the point that they can overwhelm the ecosystem of an aquarium. 

Related article: Why are my snails dying?

Where do snails come from? 

Most snails in aquaria come in with aquarium plants, although they may accidentally be transported as an egg in water alongside a fish. Small, clear eggs on the undersides of plant leaves are often difficult to spot, and may take up to a month to hatch out, so you won’t even initially spot the young. 

Plants taken from a local pond are especially notorious for bringing in tadpole and ramshorn snails. 
Once you have some, snails can be transferred between tanks through nets, wood and rocks, gravel, and even filter media. 

How do so few become so many? 

Snails multiply because of an underlying problem with the aquarium they’re in. In order to grow and reproduce, any aquarium snail needs a supply of food, and a poorly maintained tank, or a tank that is routinely overfed, has exactly the kind of food they’re looking for. 
Uneaten fish food, fish faeces, algae, and dying plants are a dream come true for nuisance snails, and in the presence of these organic wastes they will go forth and multiply.  
You might only need a single snail to get into the tank to generate hundreds more. Tadpole snails may be carrying eggs when they arrive, and will quickly lay them somewhere out of sight. Malaysian trumpet snails are livebearers that may arrive carrying young, and these young will remain hidden in the substrate until food starts to run out and they have to visit the surface. 

Are aquarium snails bad?

Snails both are and aren’t a problem. On the one hand, if they weren’t there, eating all of the waste in the tank, you could be facing a much more severe problem of poor water quality. In the short-term, they’re actually something of a safety buffer, stopping your fish from being poisoned by the likes of ammonia spikes. Unfortunately, in the longer-term, snails also contribute their own waste to the tank, and the more of them there are, the more waste they’re going to produce. The combination of poor tank maintenance or overfeeding, with an excess of snails, results in a drain on the tank’s oxygen content. That in turn can start to affect fish or beneficial filter bacteria.
In large numbers, they also present a clogging hazard. Filter inlets and even filter media can be plugged with tiny snails when the numbers become too great. 
Snails are largely inevitable in an aquarium, and the real trick is to use them as a guide to your aquarium maintenance. If you only ever see one or two, that’s a good sign that you’re keeping on top of your tank’s hygiene. If you see dozens or more at a time, something has gone wrong that needs to be addressed. 

Some aquarists with sand substrates appreciate a few Malaysian trumpet snails in the tank, as these burrowing gastropods help to aerate the substrate.

How do I control snails in my fish tank? 

Once you have snails in a tank, it’s usually the case that you will always have snails in that tank. Eradicating every single one, including the eggs, is difficult at best. But what you can hope to do is manage the numbers. 

Clean the tank

Making things more hygienic in your aquarium should be your first response to a snail outbreak. Water changes alone won’t do the job, because it’s the solid organic waste that you’re aiming to remove. By removing the food sources for the snails, you instantly limit their ability to grow reproduce. Starve them out. 
Begin with a good substrate clean with a gravel cleaner and siphon. If you have gravel in your tank, be sure to push the gravel cleaner right to the bottom and get all the muck out—the snails will dig down for it if you don’t. Try not to change too much water in one go, and if you can’t clean the gravel without getting lots of water out, try spreading the cleaning over four or five days, concentrating on a different section of the tank each time and limiting the amount of water removed to around 30%.

If for any reason you don’t want to remove water while cleaning the substrate, consider an in-tank gravel vac that recirculates the water. 
Algae should be cleared away, as the snails will feed on this too. Use a hand-held algae pad and make sure you get right down to the level of the substrate, and into the corners of the tank. If the tank is too deep to reach in to, consider a magnetic algae scraper, or an algae pad with a long handle. These will take longer to use to carry out a thorough job. 
Also look at your plants. Any dead or dying leaves will need to be chopped off as these are a snail’s paradise. Use long aquascaping scissors if you can’t reach down with a pair of manicure scissors or household scissors. Don’t try to simply tear dead leaves off as this will damage the plant, leading to more dead tissue and more potential snail food. 

Use a snail trap

Once you’ve cleaned the tank, you’ll still have an excess of snails, and these need to be removed before they starve, die, and pollute the water. 
One method is to use an off-the-shelf snail trap, such as the JBL Limcollect II, available from many aquarium retailers. These snail traps are baited with a tablet of catfish food and placed in the tank overnight. The small, lifting flaps allow snails to enter but not leave, while the opening is too small for the likes of Corydoras catfish to blunder into. 
Alternatively, you can improvise with a saucer, a plant weight (or a teaspoon) and a piece of courgette. Simply weigh a slice of courgette down with a weight (or skewer it on to the spoon) and place it into the middle of the saucer. Now place the saucer into the middle of the aquarium and leave it for a few hours in the dark (either at night, or by turning the tank lights off for a while). When you return to it, the saucer will be covered in snails that you can then (carefully) remove and dispose of.
Snail traps will need to be used repeatedly until the snail population has been brought back under control. 

Buy a snail catcher

If your snails are bold enough to be out and about during the day, the Dennerle Snail Catcher is a great way to remove them from the glass. Working something like an old manual-powered lawnwomer, you simply roll the catcher over any snails climbing over the glass, which are then rotated around the device and collected in a trap at the front. 
Limitations to this are that it only works against snails that are on glass, and only on snails that you can see. If you have an infestation of Malaysian trumpet snails, it’s not the best option, as these snails not only prefer the substrate to climbing on glass, but are nocturnal and unlikely to be out and about while the lights are on.

Cut back on feeding

More snail outbreaks than not are caused by overfeeding fish, and feeding fish on the wrong foods. Offering fine, powdery flake food to fish with big mouths results in lots of uneaten mess, while offering sinking foods to fish that surface feed will result in meals sitting where they can’t reach them. Make sure you’re matching the right food to the right fish. 
Even with the right foods, most fish will only need one small feed a day. Either try cutting back the amount offered at each feed, or consider one or two fast days a week where the fish receive nothing. 
Most fish are gluttons and are happy to eat until their guts are bulging. The problem here is that they don’t need that much food, especially if they’re getting a meal every day. Dried foods are rich in nutrients, and if a fish is bloated it’s unlikely to even extract all of the nutrients from its meal, passing many of them out with its faeces later on. 
Unless you have a species with a niche or specific feeding requirement, offer as much food as a fish will eat in around a minute, or until the bellies look comfortably full. Any more than this is just feeding the snails. 
Of course, any leftover food sat in an aquarium must be removed after you’ve conducted a feed. Either a net or a gravel cleaner and siphon can do this, though aquarium hoovers are also available.

Try adding assassin snails

Assassin snails (Anentome helena) are smallish (3cm), affordable, and attractive snails that are highly predatory, active hunters. Their natural diet includes worms and other snails, but in the aquarium they can be a mixed bag of success. 
In a tank with an extreme snail infestation, the nuisance snails are likely to continue breeding and growing at a faster rate than a few assassin snails can tackle them. There’s also the problem that if the tank containing assassin snails continues to be overfed with meaty foods such as bloodworm, the assassins will eat these as the ‘easy option’ rather than hunting down their dinner. 
Assassin snails can help to control a nuisance snail population when added in sufficient numbers, but the problem then is that you’re just swapping one snail infestation for another. Assassin snails are equally prone to breeding in a tank when conditions are right for them (by which I mean that there are abundant nutrients), and so sometimes the solution to snails isn’t adding more snails. 
One final problem with assassin snails is that they have been known to eat shrimplets. If you’re trying to breed shrimps, they are not for you.

Outcompete with ornamental snails and shrimps

Where some slight overfeeding is an unavoidable problem (you might have messy feeding catfish, or fry, for example) it is wise to add a more desirable ‘clean-up crew’ to the tank. 
Aquarium shrimps like Amano shrimp are an excellent choice in cleaning up uneaten bits of flake, but some species will even compete with snails for algae and biofilm as well. Likewise, ornamental snails such as rabbit snails will compete with nuisance snails for a food source.

The only real downside is that when you have invertebrates in a tank, it can become more difficult to treat disease outbreaks in fish—many inverts react badly to certain fish medications.

Can I just crush snails? 

As infuriating as they can become, don’t be tempted to squish snails against the glass as and when you spot them. Each dead snail represents a bundle of meat sat in the tank, which will either decay (ruining water quality) or just be recycled by the remaining snails in the tank. 

Will fish control a snail outbreak? 

Various fish are lauded for their snail-eating tendencies, but it’s not as simple as tossing some in and hoping for the best. 
The first problem is a water quality one. Remember, there’s a snail outbreak because of a hygiene issue in the tank, be that a lack of gravel cleaning, overfeeding, or decaying plant matter. Until these initial problems have been resolved, all an extra fish is doing is contributing to making even more waste in the tank. Get the husbandry in order first, and then (and only them) consider a fish to help clear up the stragglers. 
Not all fish are good choices. Clown loach (Chromobotia macracanthus) are often marketed as snail munchers, but these fish need to be kept in shoals and can grow large. Adult clown loach may reach a massive 40cm, and need aquaria several metres long to house them. 
A smaller snail-eating loach is the dwarf chain loach (Ambastaia sidthimunki), that reaches around 6cm long, and, unlike many other loaches, doesn’t become an eye-nipping nuisance when it grows a bit larger. On the downside, dwarf chain loach are expensive fish (starting around £10-£15 each) and need to be kept in a shoal of ten or more fish. They are also sensitive to poor water quality, which tend to go hand in hand with snail outbreaks. 
Many pufferfish are known snail eaters, and have impressive ‘beaks’ to help them crush through the hard shells. Sadly, many pufferfish also won’t think twice about using those same beaks on their soft, meaty tankmates, and won’t spare a thought for any shrimps they encounter and eat. There are also issues with some pufferfish having brackish (partially saltwater) origins, making them unsuitable (biting aside) for freshwater community tanks. 
One safer option is the pygmy puffer (Carinotetraodon travancoricus), which is a largely peaceful, dwarf species that reaches around 3cm long in tanks. These puffers will seek out and eat any snails in the tank, but can occasionally also turn on peaceful tankmates—especially those with long fins. 
Other noted snail eaters include Anomalochromis cichlids, convict cichlids, and Badis badis
The greatest problem to adding a fish to control your snail population is that if the tank is still being overfed, these fish will turn to the easy option morsels coming from the fishkeeper and ignoring the snails altogether. Why go to the trouble of breaking open shells when you already have a full belly? 

Will medications control snail populations? 

Snail medications should be approached with some caution, as while they may kill snails, they aren’t a ‘fire and forget’ solution. Aftercare is required. 
If you have 500 snails in your tank and you kill them all with one powerful dose of molluscicide, you now have 500 rotting bodies in the tank. Unless those bodies are removed immediately, your tank will soon be overwhelmed with pollution. The job of removal becomes all the trickier with the likes of Malaysian trumpet snails, as these will hidden in the substrate and will require you to sift through the entirety of your sand or gravel. 
The real benefit of snail killing medications is that they can be used on any new plants you purchase. Make up a bath of snail killer and water, and leave your plants to soak in it for 24-48 hours, In this time, any unwanted hitchhikers, as well as their difficult-to-see eggs will have perished. Now rinse the plants and add them to the tank.