Onion snail care guide

1How big do they get?

The UK wholesaler gives about 25 mm shell diameter. This is width, not height. An orange or spotted shell alone is not a reliable species test; ask for the scientific name.

Adult shell size

Varies Up to about 25 mm shell width in the UK wholesaler’s account; individual sizes differ. Fact source

2How long do they live?

The supplier estimates 1–2 years. Some care accounts report longer lives, so use this conservatively; the age of a purchased adult is often unknown.

Lifespan

1–2 years 04 years Conservative supplier estimate; longer lives are reported elsewhere, with age at purchase usually unknown. Fact source

3What do they eat?

Give access to established algae and biofilm on stones, wood and glass. Prepared foods may be refused, so a spotless new aquarium can leave this grazer hungry.

Diet type

Herbivore Algae and biofilm specialist; prepared food may be refused. Fact source

4Do they eat plants?

Healthy plants are normally left intact while surface growth is grazed. This is a useful distinction from the plant-eating great pond snail, which you can compare in the Index.

Plant eating

No Healthy plants normally left intact. Fact source

5Do they eat algae or clean the tank?

A strong grazer of soft surface algae and biofilm. It will not reliably clear every algae type; keep enough edible growth available.

Algae role

High Surface grazing is central to feeding; not every algae type is eaten. Fact source

6What eats them?

Exclude puffers, snail-eating loaches, assassins and predatory crustaceans. Peaceful appearance or a larger shell does not make those pairings safe.

Predators

Puffers, snail-eating loaches, assassin snails and predatory crustaceans. Crustaceans: Aquarium Dietzenbach compatibility guidance. Fact source

7Are they safe with shrimp, fish and other snails?

Peaceful shrimp can work when water needs overlap. Avoid predators and too many competing grazers. Use the nerite variation link for the broader group guide; this page covers the onion type.

With shrimp

Yes Peaceful shrimp with compatible mineral and temperature needs. Fact source

With fish

Caution Non-predatory fish only. Fact source

With other snails

Caution Peaceful snails only; exclude assassins and avoid grazing competition. Fact source

8How many per tank?

Use 45 litres for one as the more spacious supplier starting point, with abundant grazing. J&K lists 20 litres; food availability and companions decide suitability, not volume alone.

Starting tank volume with conditions

45 litres Starting suggestion for one in a mature tank with plentiful algae and biofilm; extra grazers need more food and space. Fact source

9Do they need a heater, or can they live in cold water?

Use 22–28°C following the UK supplier. A heater is needed where room conditions cannot maintain a stable suitable temperature.

Recommended water temperature

22–28 °C 1530 °C Fact source

10What water do they need?

The UK guidance gives pH 7.2–8.2 and GH 10–25°dGH. Check compatibility before adjusting minerals; this is general hardness, not KH.

pH

7.2–8.2 pH 69 pH Fact source

Hardness guidance with units

GH 10–25°dGH in the UK wholesaler’s guidance; stable mineral-rich water. Fact source

11How do they breed, and how fast?

There are separate males and females. They may lay eggs in freshwater, but the larvae need a saline development phase. Adding salt to a community tank is not a breeding method.

Can reproduce in a freshwater aquarium

No Egg capsules may be laid; larvae do not complete development in ordinary freshwater. Fact source

Breeding speed

Not applicable No normal freshwater recruitment; this does not mean no eggs. Fact source

Pair needed

Yes Separate sexes for fertilisation; a pair alone does not make freshwater breeding possible. Fact source

12What do the eggs look like, and how long do they take to hatch?

White, hard capsules attach to décor and other firm surfaces. They are not evidence of an impending freshwater colony. A simple hatching countdown would misrepresent the larval stage.

Reproduction type

Egg laying Fact source

Hatching time

Not applicable No freshwater baby-snail countdown: a saline larval phase is needed. No validated species-specific incubation schedule is supplied here. Fact source

13Are they good or bad, and how do I get rid of them?

Freshwater population growth is low, though egg capsules may be unwelcome. Consider that before adding one; buying more to remove algae also means more mouths to feed. Never release aquarium snails outdoors.

Population growth concern

Low Low population growth in freshwater; visible egg capsules are still possible. Fact source

14Are they nocturnal, and why do they hide?

Often more active after dark, with daytime grazing possible. Check behind décor before assuming it escaped. Regular burrowing has not been established by the reviewed species sources.

Active time

Night Often more active after dark; daytime grazing also occurs. Fact source

Burrows

Not known The species guide describes hard-surface grazing, but does not establish whether individuals regularly bury themselves. Fact source

15Can they survive out of water or climb out?

Use a secure, ventilated lid and close cable gaps. Check the rim when one disappears; these snails can leave the water.

Secure lid needed

Yes Cover escape gaps while retaining ventilation. Fact source

16Is it dead, or just not moving?

Rest and hiding can resemble inactivity. Check water and available grazing first; investigate lasting changes without forcing open the operculum.

17Why is the shell damaged, and do they need calcium?

Suitable mineral content supports shell growth. Review pH, hardness and feeding if erosion appears; avoid sudden mineral additions.

Calcium required

Yes Fact source