Why Do Snails Die in an Aquarium? Causes to Check

The short answer

Common causes of snail deaths include copper from fish medications, soft water short on the calcium their shells need, ammonia or nitrite, a sudden change in water chemistry when they are added, and too little food. Some simply reach old age; Aquarium Breeder puts most aquarium snails at 1 to 3 years, and figures differ by species (see below). Test the water first.

Snails can die in tanks where the fish look fine. LiveAquaria, an online livestock retailer, says: “Aquatic life such as fish, and especially invertebrates (including corals), are very sensitive to even minor changes in water chemistry.”

This guide covers freshwater tanks and water-side causes only; reef keepers should follow their salt mix maker and livestock supplier. If snails keep dying, or your fish look unwell too, test the water now and contact an aquatic veterinarian.

First, make sure the snail has died

Aquarium Co-Op, an aquarium retailer, says that if a snail “has not moved in 24–48 hours, consider picking it up to see if it reacts”, and that an overpowering stench means it has died. Three things can look like death:

Floating. Aquarium Co-Op explains that mystery snails have both gills and lungs, and “Holding air in the lungs causes the snails to float”. Our guide to why snails float in an aquarium covers the other reasons.
Lying upside down. Aquarium Co-Op says mystery snails “can easily right themselves if they land upside-down”, and nerite snails can too “unless other animals are constantly picking on them”.
A new arrival that looks lifeless. LiveAquaria says “Some fish and invertebrates can appear dead when they arrive and will usually revive when the acclimation procedure is followed correctly.”

Aquarium Co-Op’s nerite guide says: “If your snail is hanging out of its shell or has an unpleasant smell, remove it from the tank so that the body won’t cause a toxic spike in ammonia or nitrite.”

Quick check

Then test ammonia and nitrite. Aqueon, an aquarium maker, says in its freshwater water-quality guide “The only safe ammonia level is zero.” and “The only safe nitrite level is zero.” API, a test-kit maker, says: “In new aquariums, ammonia should be tested every other day until the ammonia level measures 0 parts per million (ppm) or mg/L. In established aquariums, ammonia should be tested weekly to make sure it is at a safe level.” After a snail has died, keep testing ammonia and nitrite until both read zero. Above zero, our guides to high ammonia in an aquarium and high nitrite in an aquarium cover the causes and fixes.

The usual causes at a glance

Cause	How to check	What the sources advise
Copper	Copper test; medication labels	Snails out before any copper treatment
Soft water, low calcium	GH and KH test	Raise minerals slowly; calcium-rich food
Ammonia or nitrite	Ammonia and nitrite test	Find the source (see the guides above)
Sudden change on arrival	Store pH vs tank pH	Acclimate slowly
Salt treatment	Was salt added?	Snails out first
Too little food	Algae and leftovers to graze?	Algae wafers, blanched vegetables
Tankmates	Puffers, snail-eating loaches, assassin snails	Keep apart
Old age	How long you have had it	Most 1 to 3 years, per Aquarium Breeder; varies by species

Copper from medications and tap water

The University of Florida’s IFAS Extension, a university extension service, says in its guide to copper in freshwater aquaculture and farm ponds (not an aquarium guide) that “Copper is also toxic to invertebrates, such as snails”. Its guide to copper in marine aquaculture and aquarium systems adds that the copper levels used to treat fish “are lethal for most invertebrates”. Aquarium Co-Op’s page for the Fritz copper test kit says “Many aquarium species, especially shrimp and other invertebrates, are very sensitive to even the slightest bit of copper in the water”, and mentions traces in tap water and “strong copper-based medications”.

Take snails out before any copper or salt treatment

Aquarium Co-Op says mystery snails “are sensitive to salt and copper-based medications, so please remove them if the aquarium is being treated with those chemicals.” UF IFAS’s guide to copper in marine aquaculture and aquarium systems says “Invertebrates should be removed prior to treatment with copper.” This guide gives no treatments or doses; for sick fish, contact an aquatic veterinarian.

Test the tank for copper

The Fritz Copper Test Kit, which its Aquarium Co-Op page says “Measures free and total copper in fresh and salt water”, is one example. The same page says: “If you suspect traces of copper in your tap water or you are using strong copper-based medications to treat your tank, make sure to use the Fritz Copper Test Kit.” If the test shows copper, the same page’s rule is that levels be “back to 0 ppm before adding back the invertebrates”, so keep living snails out of that water until the kit reads zero; for where to hold them, ask your livestock supplier.

Bring copper down before snails go back

The same page says: “To decrease copper levels, perform partial water changes and/or use copper-adsorbing resins or filter media until the copper level consistently shows zero ppm with this kit.” For each change in a freshwater tank, Aqueon says: “Always treat tap water with a water conditioner to neutralize chlorine and ammonia before adding it to the aquarium.” and “Replacement water should be the same temperature as the aquarium water.” It also says to “Avoid water changes of more than 25% as larger water changes can stress your fish and upset the balance in your aquarium.” Saltwater keepers should follow their salt mix maker. Keep testing: UF IFAS, writing about marine and aquarium systems, says levels “should be checked regularly for several weeks afterward, in case of copper leaching”.

Warning

Aquarium Breeder, a shrimp-keeping hobby blog, says: “There are commercial products that kill snails. Use them as a last resort, and only in tanks without shrimp or other invertebrates you want to protect.” If one has been used in your tank, read its label and follow the maker’s warnings.

Soft water and weak shells

Practical Fishkeeping, a fishkeeping magazine, writing about soft, acidic blackwater habitats, says calcium matters for “the growth and strengthening of a snail’s shell”, and “When levels drop, or are naturally lacking, snail shells can erode, crack or discolour”. Aquarium Co-Op says mystery snails “cannot live in soft water environments” and “require lots of calcium and other minerals in their water and diet to grow a healthy, smooth shell”.

A GH and KH test shows where your water stands. API says “General hardness is the measure of calcium and magnesium ion concentrations dissolved in water” and “soft water is low in these minerals”. It adds: “An aquarium with a low KH level will tend to be acidic. Aquariums with very low KH are subject to rapid pH shifts if not monitored carefully.” The API GH & KH Test Kit is one kit that reads both. No maker page used here gives a GH target for snails. Our guide to why aquarium pH keeps dropping covers the pH side.

Aquarium Co-Op’s nerite guide says: “If you have soft tap water and notice your snails are getting cracked or eroded shells, increase the minerals in their water and food to keep the damage from progressing.” It uses crushed coral and mineral supplements. Aqueon describes crushed coral and dolomite gravel as calcium carbonate gravels that “slowly dissolve over time, raising and buffering pH”. Aqueon, writing mostly about fish, is more cautious: “Unless you are trying to breed sensitive or wild caught fish from environments with extremely low or high pH, it is best not to try to change your aquarium pH.” It adds: “If you already have fish or other creatures in your aquarium, never make sudden or drastic changes to pH or any other water parameters.” Follow the label of any mineral supplement, and check that your fish suit harder water: Aquarium Co-Op keeps mystery snails with fish “that are also compatible with higher pH and harder water”.

Ammonia, nitrite and a rough arrival

The US EPA, a federal agency, based its 2013 ammonia criteria for wild fresh waters partly on “the effects of ammonia on sensitive freshwater gill-breathing snail species”. In a tank, Aqueon’s figure is zero, and if you raise pH for shells, Aqueon notes that “Ammonia is more toxic at higher temperatures and pH levels above 7.0”.

Aqueon’s pH guide says: “When purchasing new fish or invertebrates, compare your aquarium’s pH to the water in the tanks you are buying them from.” It advises acclimating “by slowly adding small amounts of your aquarium water to the bag or shipping container until the pH is as close as possible”, and says “The greater the difference, the more gradually they should be acclimated”. Floating the sealed bag, LiveAquaria says, “allows the water in the specimen bag to adjust slowly to the temperature in the aquarium”, so floating alone matches temperature, not pH.

Aqueon notes that “as water warms up it holds less oxygen” and suggests an aerator “to improve gas exchange at the surface”. In the wild, UF IFAS says, Florida’s applesnails, including the spike-topped applesnail that Aquarium Co-Op calls the mystery snail, “are not known to withstand water temperatures below 10°C (50°F)”. If the thermometer drifts, see why an aquarium heater stops working.

Hunger, tankmates and old age

Aquarium Co-Op says people usually have trouble with nerites “if the nerite snails aren’t getting enough food or minerals”, and that they “can starve to death if there is not enough algae in the tank or other fish are outcompeting them for food”. It suggests “algae wafers, blanched zucchini slices, and canned green beans”, and for mystery snails, “calcium-rich vegetables like blanched spinach or kale”. Take out what is not eaten: Aqueon warns that “uneaten fish food releases toxic ammonia and nitrite as it decomposes”.

Aquarium Co-Op also advises against keeping mystery snails “with snail eaters like puffer fish, certain loaches, and turtles”, and against fish “that may try to nibble on their long antennae”. Its pest-snail guide says assassin snails “ambush and eat other snails, even those that are much larger in size”. If your problem is snails appearing rather than dying, see our guide to why snails appear in an aquarium.

Age matters too. Aquarium Breeder says “Most aquarium snails live 1–3 years.” For single species the sources differ: Aquarium Co-Op gives mystery snails “an average life span of 1–2 years, depending on the water temperature” and nerites about 1 to 2 years; Aquarium Breeder’s chart gives 1 to 3 years for both.

Ready to buy?

Our freshwater aquarium test kit roundup includes master kits and the API GH & KH kit, our aquarium snail food roundup includes calcium tablets and algae wafers, and our Water Care & Testing section gathers test kits and conditioners.

Frequently Asked Questions

Q. Is it bad to leave a dead snail in a fish tank?

Yes. Aquarium Co-Op links a dead snail’s body to an ammonia or nitrite spike, so take it out once you are sure and keep testing.

Q. What can kill aquarium snails?

Copper can kill snails: UF IFAS’s marine and aquarium copper guide says the levels used to treat fish “are lethal for most invertebrates”, and Aquarium Co-Op’s page says mystery snails are sensitive to copper-based medications. Products sold to kill snails do just that, and Aquarium Co-Op says mystery snails are sensitive to salt.

Q. Why do my snails keep dying when my fish are fine?

Invertebrates can react to water the fish tolerate; Aquarium Co-Op’s copper kit page singles out shrimp and other invertebrates. Test copper, GH and KH as well as ammonia and nitrite.

Q. Can a betta live with snails?

Aquarium Co-Op has kept mystery snails with “calmer betta fish that aren’t as aggressive”, and advises against fish that nibble at their antennae.

Sources (20)

Aquarium Tales Team

Written and reviewed by the Aquarium Tales Team. See the About page for how we work.