If you’re into snails like me, you know that mystery snails (Pomacea bridgesii) are messy and can quickly alter your tank’s chemistry. As such, keeping the correct number of snails for your tank size is key to maintaining a healthy freshwater aquarium.

So, how many mystery snails should you keep in your tank?

You can keep 1 – 2 mystery snails per 5 gallons of water, up to 4 snails in a 10-gallon tank,  and up to 8 snails in a 20-gallon tank. The number of mystery snails per gallon depends on whether or not you have tank mates, the type of filter, and how frequently you can clean and cycle the aquarium.

You can keep one to two mystery snails per 5 gallons of water.

We do not recommend a large population of snails in your tank. Mystery snails poop a lot, and their waste can cause a huge bioload or ammonia spikes that can kill your fish. However, keeping them in your tank has its benefits, including feeding on dead or decaying plants, dead fish, algae, and biofilm.

Below, I’ve compiled a detailed guide on stocking mystery snails in your tank, important considerations, and how to control their population to avoid overstocking.

Mystery Snails and Tank Size

The rule of thumb is to keep 1-2 mystery snails per 5 gallons of water. You can keep slightly more snails in the tank, but it is totally up to you and the amount of work you want to put into cleaning and cycling the tank.

The minimum tank size recommended for mystery snails is 5 gallons. You can keep around 1-2 mystery snails in a 5-gallon tank. A 10-gallon tank could accommodate 2-4 mystery snails, while a 50-gallon tank could accommodate up to 20 mystery snails.

Here’s a table with general mystery snail stocking recommendations for different aquarium sizes.

Tank sizeNumber of mystery snails
5 gallons1 to 2 snails
10-gallon tank4 snails
20-gallon tank8 snails
30-gallon tank12 snails
40-gallon tank16 snails
50-gallon tank20 snails
75-gallon tank30 snails

Note: We do not recommend keeping mystery snails in tanks smaller than 5 gallons. While some recommend 1 snail in a 2.5-gallon tank, I believe it is not the best home you can give your pet.

5 gallons

A 5-gallon tank is the smallest tank recommended for mystery snails. You can keep two snails in the tank and have a few tank mates. If it is a planted tank, the space will be limited, so consider cleaning and cycling the water weekly or bi-weekly.

If you don’t have enough time to clean the tank twice a week, keep only one mystery snail in a 5-gallon tank to reduce the bioload and keep the aquarium healthy.

10-gallon tank

You can keep up to 4 mystery snails in a 10-gallon tank. The ideal number is two snails, but if there are tank mates and a standard filter in the setup, the bioload can easily threaten the health of your aquatic pets.

With 4 snails and some fish in the aquarium, I recommend cleaning the tank and cycling the water at least once a week to prevent ammonia spikes.

20-gallon tank

The ideal number of mystery snails in a 20-gallon tank is 8. However, depending on the filtration system and your dedication to maintaining the tank, you can keep a few less or a few more snails in this tank.

30-gallon tank

A good estimate is to have one mystery snail per 2-3 gallons of water. Therefore, a 30-gallon tank could comfortably house around 10-15 mystery snails.

Mystery snails enjoy bigger spaces with enough algae, biofilm, and decaying vegetation to feed on. If your tank does not have enough vegetation, provide algae wafers or vegetables like lettuce, cucumber, kale, and spinach. 

Remember to be careful about how often you feed them since mystery snails can overeat and grow overweight.

What affects the number of mystery snails

As I already mentioned, the number of mystery snails that can be kept in an aquarium depends on various factors such as the size of the snails, the number of other tank mates, the type of filtration, and your willingness to perform frequent water changes.

Tank mates

Mystery snails are generally peaceful creatures and can live with other peaceful tank mates. The number of tank mates in the aquarium reduces the number of mystery snails you can stock per gallon of water.

Overcrowding the tank with too many fish and snails leads to an increased bio-load, which can negatively impact the water quality and limit the number of snails to keep.

You also want to consider that these snails are prolific at reproducing and can overpopulate a tank quickly.

Plants and other aquarium decorations

Plants and decorations are important in aquariums. In fact, plants also help reduce the aquarium’s bioload, but having too many of these decorations can limit the number of snails and fish to stock.

Filtration system

The type of filtration system you have in the tank is really important to the number of snails you can keep in your tank. For example, you could have as many as 30 – 50 snails in there if you so choose, but unless you are willing to use heavy filtration and weekly or even bi-weekly water changes, you will not have a healthy tank.

Water cycling and tank cleaning frequency

More snails mean a bigger workload. For people willing to clean their tanks weekly or even bi-weekly, you can stock a slightly higher number of snails.

Sometimes, mystery snails try to escape the tank when their environment isn’t pleasing. As you know, the chances of mystery snails surviving out of the water are low. Without moisture, they easily dry out and die.

Mystery snail population control

Mystery snails can lay up to 300 eggs at once, and about 50-100 hatch. If these many eggs hatch in the tank, you’ll have a population breakout in the tank. Some varieties of mystery snails are seen as invasive species whose population is hard to control.

To accommodate the growing population of mystery snails, you need an additional tank and an increased supply of food for the baby snails. As a consequence, the bioload of the tank will also be higher.

Population control is key for your tanks; otherwise, you’ll end up with nitrite spikes that can kill all your aquatic pets. Here are a few ways to control the population of mystery snails in your tank:

1. Keep one gender of mystery snails

Checking the gender of mystery snails is not easy, yet it is a great way to separate them and help control their population in the tank. Keeping mystery snails of the same gender will ensure fertilization does not occur. Female snails will lay unfertilized eggs that’ll not hatch, meaning you can keep the number of mystery snails per gallon of water constant.

2. Raise the water level to just below the top of the tank

Mystery snails lay their eggs above the waterline, and the clutches of eggs must remain above the water surface. If mystery snail eggs fall in water and stay inside for long, the embryo will drown and die.

I find that raising the water level to just below the top of the tank to discourages the female snail from laying eggs. It is not the best solution for controlling the number of snails in the tank, but it works as you find a better fix.

3. Remove the eggs from the tank

Mystery snail eggs require a temperature of 73.4°F to hatch. Therefore, if you do not need them to hatch, you can remove them from the tank and keep them in a cold environment.

I recommend removing both fertile and infertile snail eggs to keep your tank clean and healthy.


I recommend 1 mystery snail for every 5 gallons for slightly less maintenance (water cycling and cleaning), but you can keep two if you don’t mind a bigger bioload and more frequent water changes.

It really comes down to how much you want to clean. First off, they need proper nutrition. Calcium and protein. Second, they poop a lot. In my experience, the heavy bioload in my breeder tanks forces me to clean every 3-4 days. I clean my grow-out tanks once a week.

If you feel you have stocked slightly more mystery snails in your tank, ensure you have heavy filtration in your aquarium and do frequent gravel vacuuming to keep the tank clean and safe for the snails and other aquarium inhabitants.

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