How to get rid of pest snails

Where they come from

Nobody goes to the fish store for bladder snails. They come home as a few eggs on a stem plant or in a clump of moss, and two months later the front glass looks freckled. Live plants bring them into most tanks sooner or later.

A few small snails do no harm. They eat leftover food, algae film, and melting leaves, and Malaysian trumpet snails turn over the top inch of sand. They become a problem when dozens cover the glass every night, when they clog a filter intake or a shrimp tank's sponge, or when you want them gone. Their numbers track how much food the fish leave behind.

Which snail you have

Bladder snails (Physella acuta) have a thin, see-through brown shell up to about half an inch long. Hold one point up with the opening facing you and the opening is on the left. They move fast for a snail and lay clear jelly blobs of eggs on the glass and leaves.

Ramshorn snails have a flat coiled shell, red, pink, or brown, usually under an inch across. They lay flat jelly discs. They eat melting leaves and leftovers and mostly leave healthy plants alone.

Malaysian trumpet snails (Melanoides tuberculata) have a long pointed cone shell with dark flecks, about an inch long. They live in the substrate and come out at night, so a tank can hold hundreds before you notice. They give birth to live young, which means there are no egg clutches to scrape.

A big gold, blue, or ivory snail that lays pink clutches above the waterline is a mystery snail. Its clutches are easy to spot and peel off. Nerite eggs are hard white dots that don't hatch in fresh water. Neither one takes over a tank.

Feed less first

Every pest snail in the tank lives on food the fish missed. Feed what the fish finish in about two minutes, once or twice a day, the same rule as the feeding guide. Drop bottom-feeder wafers after lights out and take out what's left in the morning. Vacuum the gravel at each water change so old food doesn't build up under the surface.

Snail numbers drop on their own once food runs short, but it takes two to three weeks to see. The steps below speed that up.

Trap them overnight

Snails are most active after the lights go off. At bedtime, set half a sinking wafer or a slice of blanched zucchini or lettuce on a saucer or inside a snail trap on the substrate. Blanch vegetables for about a minute in boiling water so they sink. In the morning, before the lights come on, lift it out with the snails on it.

Repeat every night for one to two weeks. A badly overrun tank can give up dozens a night at first. If the morning count keeps falling, the feeding cut is working. Lift the trap first thing in the morning, before snails crawl back out.

Pick them off by hand

Pick snails off the glass with your fingers when you see them. Long tweezers reach the ones on plants and hardscape. Scrape jelly egg clutches off the glass with an algae scraper or a razor blade and net out the bits.

Trumpet snails are the hardest to get to zero because they hide in the sand. Trap at night and vacuum a little deeper at water changes. A few left in a sand bed keep it stirred, so thinning them out is usually enough.

Seal the snails you remove in a bag, freeze it, and put it in the trash. Don't flush live snails or tip them into a pond or creek.

Snail-eating snails and fish

Assassin snails (Anentome helena) eat other snails. They grow to about an inch, have a cone shell with yellow and brown stripes, and leave fish alone. Three to five in a 20 to 30 gallon tank will thin out bladder or ramshorn snails over a few months. They lay one egg at a time, so they don't become the next infestation. They can kill small nerites and young mystery snails, though.

A pea puffer clears snails fast. It also eats shrimp and nips fins, so it belongs in its own tank. Add one only if you were planning a puffer tank anyway, and then the pest snails become free food. Clown loaches are the usual shop suggestion. They grow close to a foot long and live in groups, so they need a much bigger tank than most snail problems come with.

Skip copper snail killers

Many snail-killer products contain copper. It kills every invertebrate in the tank, including cherry shrimp, nerites, and mystery snails, and it can stay in the substrate long after the dose.

A chemical kill also leaves hundreds of dead snails rotting in the gravel at once, which can push ammonia up within a day or two. If you've already dosed one, vacuum the substrate hard, change water, and test ammonia every day for a week.

Keep the next batch out

New plants are the usual way in. A bleach or alum dip and a week or two in a tub catches adults and eggs, and the plant quarantine guide has the times and ratios. Tissue-culture cups arrive snail-free. Pour shop water down the drain, never into the tank, and rinse nets and tweezers between tanks.