How Many Mystery Snails In A Tank? (1-75 Gallons)

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As I started raising mystery snails as a pet, I quickly realized the importance of the number of snails to keep in one tank at any given time. That struck me after the severe outbreak I experienced in my aquarium. As time passed, I learned how many mystery snails should be per gallon and how to prevent overpopulation.

Each mystery snail requires two and a half gallons of water. For example, 20-gallon tanks can hold up to eight mystery snails, while 10-gallon tanks can accommodate merely four. However, it is generally recommended to have extra space since mystery snails multiply rapidly.

As we move forward, I will list how many mystery snails you should have in your aquarium while considering all different sizes. Then, I will show you a few tricks to prevent outbreaks and control the snails’ population.

How Many Mystery Snails Should Be In A Tank?

Mystery snails have their uses. People usually keep them because they eat algae. However, mystery snails are only useful if you keep them in the correct numbers. They can become a problem if you allow their population to expand to dangerous levels.

The size of your mystery snail population has to match the size of your aquarium. Aquarists are expected to keep roughly two snails for every five gallons of water.[1] You can use that rule to determine the correct number of mystery snails to keep in your tank. For instance:

Small-Sized Fish Tanks:

  • 1-Gallon tanks can hold zero mystery snails.
  • 2-Gallon tanks can hold zero mystery snails.
  • 2.5-Gallon tanks can hold one mystery snail.
  • 3-Gallon tanks can hold one mystery snail.
  • 3.5-Gallon tanks can hold one mystery snail.
  • 5-Gallon tanks can hold two mystery snails.
  • 6-Gallon tanks can hold two mystery snails.
  • 6.5-Gallon tanks can hold two mystery snails.
  • 7-Gallon tanks can hold two mystery snails.

Medium-Sized Fish Tanks:

  • 10-Gallon tanks can hold four mystery snails.
  • 15-Gallon tanks can hold six mystery snails.
  • 20-Gallon tanks can hold eight mystery snails.
  • 29-Gallon tanks can hold twelve mystery snails.
  • 30-Gallon tanks can hold twelve mystery snails.
  • 36-Gallon tanks can hold fourteen mystery snails.
  • 37-Gallon tanks can hold fourteen mystery snails.

Large-Sized Fish Tanks:

  • 38-Gallon tanks can hold fifteen mystery snails.
  • 40-Gallon tanks can hold sixteen mystery snails.
  • 55-Gallon tanks can hold twenty-two mystery snails.
  • 60-Gallon tanks can hold twenty-four mystery snails.
  • 75-Gallon tanks can hold thirty mystery snails.

Remember that you don’t have to strictly follow the ‘2 Snails Per 5 Gallons’ rule. This is because it fails to consider various factors, including the space that objects like filters, plants, and pots occupy in the aquarium. The rule is designed to provide a basic estimate of the maximum number of snails a tank of a particular size can accommodate.

Try to stay under the figures stated above. For instance, even though the list says that 37 gallons can accommodate 14 snails, you are better off keeping less than 14 snails in a 37-gallon tank. Try to buy the biggest tank you can find. Mystery snails do not mind living in oversized tanks. But you will definitely cause distress if you force them to live in an undersized tank.

Do Mystery Snails Multiply?

Mystery snails tend to multiply at a rapid pace. As the female is ready to spawn, she will rise above the surface and lay a clutch of eggs, resembling a honeycomb. The eggs will hatch after two to three weeks, producing between 20 to 40 healthy adult snails.

Many people accidentally introduce the creatures to their tanks by carrying snails and their eggs into the aquarium on new plants. You can also scoop them into a bag along with new fish whenever you visit an aquatic store.

Some people hate them because a snail infestation is quite unsightly. Besides clogging filters, they will also eat your plants. Fortunately, this issue is mainly a concern where pond, ramshorn, and trumpet snails are concerned.[2] These types of snails have a reputation for multiplying wildly.

That is not true for mystery snails. They do not multiply as readily. In some cases, mystery snails will go for months (2-3 months) without laying eggs. But even if your snails are laying eggs every single week, that doesn’t necessarily make them a threat.

Yes, they can lay as many as 400 eggs.[3] But only a fraction of those eggs (30 or so) will hatch in two to three weeks. Additionally, female snails cannot breed alone. You need both genders in the tank to produce new mystery snails.

Female snails can lay eggs without a male snail, but they won’t be viable. In other words, unless you have both male and female mystery snails, their population won’t grow. Admittedly, some female snails can store fertilized eggs. 

They can lay those eggs later on after you have removed them from the tank in the store and introduced them to an aquarium in your home that doesn’t have any male snails. But once that batch of eggs is laid, if you can remove the male offspring, the mystery snail population will stop growing. 

As you can see, it doesn’t take much to control the number of mystery snails. Of all the snails that people struggle with because of the rate at which they multiply, mystery snails are one of the least problematic.

Can You Have Too Many Mystery Snails In a Fish Tank?

You can have too many mystery snails in a tank. A large population of snails is not recommended. So many snails will increase the bioload, encouraging frequent spikes in toxins like ammonia that require equally frequent maintenance procedures to control.

Not only will the conditions deteriorate at a faster rate, but the mystery snails will suffer as a result. They will come under attack from all manner of parasites and infections that thrive in poorly maintained tanks.

Even if you have the time and patience to maintain a small tank, the overcrowded conditions will make the aquarium a stressful and more dangerous environment for the mystery snails, mainly if their tankmates include larger fish with an aggressive streak.

If the mystery snails survive the deteriorating conditions in the tank, they will destroy the plant life. Yes, they eat algae. But the algae in a small tank cannot satisfy a large population of snails. Once all the algae are gone, they will turn their attention to the other plants, which you do not want.

This is why aquarists are encouraged to get the largest possible tank for their snails. If you don’t have the financial means to get a bigger tank, take steps to prevent the mystery snail population in your tank from growing out of control.

How Do You Control The Population Of Mystery Snails?

Some people think that controlling the snail population in their tank is a simple matter of controlling the number of snails they buy. But that isn’t enough. At the end of the day, if you have both male and female mystery snails in the tank, they will keep reproducing until their numbers overrun the aquarium.

You have to take more deliberate steps to keep their population under control, including:

1. Stick To One Gender

This is technically the most straightforward solution. Mystery snails cannot reproduce unless you have male and female snails in the tank. Therefore, if you can restrict the population of mystery snails in your aquarium to a single gender, you can prevent the number of mystery snails from growing.

However, this tactic only works if you can differentiate between male and female mystery snails, which is easier said than done, especially for beginners. Generally, male snails do not grow as quickly as female snails. They also have a larger shell with a rounder opening and a penial complex on their genitalia.[4]

Beginners may have a difficult time identifying this protrusion. This is why you are better off asking the retailer to give you snails of a particular gender from the start. If they know what they are doing, they will prevent you from filling your tank with mystery snails of both genders.

Either way, for your convenience, here is an excellent Youtube video that explains how to tell the gender of a mystery snail:

2. Raise The Water Level

If you don’t want to go through the trouble of differentiating between male and female mystery snails, you can take a more direct approach. Because they spend most of their time underwater, it may surprise amateur aquarists to learn that mystery snails lay their eggs above water.

This keeps the eggs out of the reach of the predators in the water. Aquarists respond to this attribute by keeping the water several inches below the top and providing some perch above the water that the snails can use to lay their eggs.

In other words, if you don’t want the snails to lay eggs, raise the water level all the way to the top. You can leave an inch or so of space. That won’t be enough for the mystery snails to breed. This will keep their numbers down.

3. Remove The Snails Manually

If it is too late to take preventative measures because the snail population in your tank is already too large, you can remove the mystery snails by hand. Pick the snails out of the tank, and keep taking them out until you are satisfied with the number left.

You can give the excess snails away to people that want them. Some stores will buy snails from people if they like the price. Though, many aquarists prefer to kill the mystery snails. This allows them to feed the remains to the fish in the aquarium.[5] The easiest way to kill a snail is to smash it with a heavy object. The method sounds harsh, but they will die instantly.

4. Take Advantage Of Predators

All the methods above require the aquarist to engage directly with the process of preventing the mystery snail population from growing out of control. But if you prefer a more hands-off approach, you can introduce fish that eat snails.

Green spotted puffers will eat snails. You can also trust clown loaches, bettas, and goldfish to eat snails.[6] If you have plants and decorations in the tank, the predators won’t eat every single snail. Some mystery snails will use the plants and decorations to hide. But the predators will eat enough mystery snails to keep their numbers down.

At the very least, you can trust them to eat the offspring of the adult mystery snails. Try experimenting with assassin snails if you don’t want to introduce fish to the mystery snail tank. They are a dangerous species that attacks and eats snails.

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As a rule of thumb, it is best to keep two mystery snails for every five gallons of water. If you want to be generous, keep one mystery snail for every three gallons of water. That way, the population will be manageable.

But the more mystery snails you have in the tank, the more problems they will cause. Aside from eating algae and plants and reproducing, they will also pollute the tank because they are dirty creatures that excrete a lot of waste.

If you want to keep mystery snails in your aquarium, start with a large tank to prevent the populations from growing out of control. Stick to one gender and keep the water level relatively high. Once you get started, you can experiment with other solutions or take a more hands-off approach by adding predators that eat snails.