The most common variety of "pest" snail is the Ramshorn snail. Apple snails (Ampullaria sp), which can grow to the size of a small grapefruit, are often
purposely introduced as part of the aquarium display, whilst Trumpet snails, with their
characteristic "cornet" shaped shell, burrow through the gravel turning it over, introducing
oxygen and preventing wastes from clogging it. Unlike their more common relatives the Ramshorn snail
and Pond snail, the Trumpet snail does not harm plants and is often welcomed by the fish keeper
as a sign of a healthy aquarium. The exception to this is the Wandering Snail
(Lymeaea ovata peregrai) which produces a poisonous substance that can cause convulsions in fish.
How do they get there?
Snails are usually accidentally introduced into aquariums when new plants are added; their jelly-like
eggs are attached to the leaves of the aquatic plants.
Snails can be prevented from entering the tank on plants by bathing the plants in Potassium permanganate
(available from pharmacists, use just enough crytals to turn the water pale pink),
or a commercial snail killer for a few hours, although once introduced, snails can be removed from the aquarium
by a number of means.
Note: Potassium permanganate is a strong oxidizer, and can cause burns to any area of contact.
It is harmful if swallowed or inhaled.
Why do they stay?
Snails thrive in an aquarium environment because there is a regular food supply. Over-feeding is
often a problem and if your snail population is increasing, you need to decrease the amount you
feed. This will not harm your fish, as the increased snail population is a sign that you are
already feeding more than necessary.
Are they beneficial?
Snails forage on left over food and graze on algae therefore a small colony should not be of
concern. In fact, they are doing you a favour by eating excess food (and can be amusing to
watch and even add to a more "natural" look in your aquarium!). Some species also help by
burrowing through the substrate thus preventing compacting and dead spots and even to help
dispose of dead fish. However, as with all living creatures, snails produce excreta and thus
large colonies of snails can result in quickly deteriorating water quality. Some species do damage
plants, and large numbers may look unsightly.
How to remove them
There are various methods of removing them, either 'biologically', physically or chemically.
If they are suited to the set-up, the best and most natural way is to add snail-eating fish. The
best candidates are usually loaches. Clown loaches are one of the most popular snail eating fish,
and usually do a good job. If your tank is not large enough for these (recommend 4ft minimum),
the smaller Pakistan or Zebra loach may be more suitable. Certain catfish like 'Dorids' (talking
catfish) or banjo catfish will also eat snails.
Another very useful 'biological' control that has entered the hobby more recently is the Assassin Snail
or Snail-Eating Snail. This snail will feed on other snails, but breeds slowly, so will not become a nuisance itself.
If the supply of snails to eat becomes depleted, they will scrounge other foods.
Even if physical removal daily can never completely wipe them out, this is a good way of keeping
the population down. "Baiting" often works - if you place a slice of cucumber or lettuce in the tank at
night (weighted down so that it stays on the substrate), the snails will congregate on it and
then you can just pull them out of the tank with the cucumber slice. One way to avoid the fish
eating the slice is to stick it inside a clean bottle, or beneath an inverted plate.
The use of any of the available chemical products is not generally recommended because anything
that can kill a snail may also be harmful to your fish and plants. Adding chemicals to your tank
is always a risky thing unless you know exactly what you are adding and exactly what the effects
will be. Most of these snail-killing chemicals use high levels of copper. A result of this method
is the massive die off of snails and the resulting decaying of their bodies. High ammonia levels
are the most likely result of this method, so be sure to follow up the treatment with a partial
water change. It may be wise to continue with at least 10% every other day for a week or more
and make sure to check the filter often during this time - daily monitoring with an ammonia and
nitrite test kit after such a treatment is also suggested.
Clearly it would be best to physically remove as many snails as possible before treating with a
Acknowledgement: Thanks to Tigerhair, for her input on this article.