5 gallon tank on window sill

Estimated reading time: 9 minutes

Wondering how many fish you can keep in your new 5-gallon tank? The simple answer: a small aquarium like yours can comfortably house 2-4 petite swimmers. This is based on the rule of thumb that says you can safely keep one inch of fish per gallon of water in your tank.

Our guide dives into the essentials of proper fish density, ensuring your aquatic pals have ample space and resources to thrive. Keep reading—your gilled friends will thank you!

Key Takeaways

  • Following the one-inch-per-gallon rule, a 5-gallon tank can house 2-4 small fish.
  • Guppy, Betta, Neon Tetra, and White Cloud Mountain Minnows are good fits for a small aquarium.
  • Avoid putting large fish like goldfish, cichlids, and angelfish in a 5-gallon tank; they need more space.
  • Regular cleaning, water changes, and using filters and heaters help maintain a healthy environment for your fish.
  • Always use water testing kits to check your tank’s water to keep your fish safe from harm.

Importance of Tank Density in Fish Keeping

Too many fish in a small space can be unhealthy for them. When there are too many fish, the water gets dirty fast. This dirt includes things like leftover food and fish poop which can make harmful chemicals like ammonia. These chemicals harm the fish, making them sick or even causing death.

Keeping the right number of fish in your tank is key to their happiness and health. A crowded tank makes it hard for each fish to find food and space to swim around comfortably. Fish also need clean water to breathe properly because they get oxygen from it just as we get air from our surroundings.

If the water is not clean, they might not get enough oxygen. Remember, healthy tanks equal happy fish!

empty 5 gallon tank

How Many Fish Can I Put in My Tank?

To figure out how many fish can live in a 5-gallon tank, there’s a simple rule of thumb: use the inch of fish per gallon guideline. This means only put as much fish length into your tank as the number of gallons it holds. So for a 5-gallon tank, you aim to have no more than 5 inches of fish. A 10-gallon tank would allow for 10 inches of fish.

Keeping fewer fish means less waste and healthier water for them to swim in. For example, if you choose small tropical fish that are about an inch long when fully grown, you could have up to five.

But if you want a betta fish, which might grow up to three inches, then it should be the only one in your tiny tank. Remember that some swimmers need more room to zoom around—even if they’re short!

Fish Suitable for a 5-gallon Tank

Celestial Pearl Danios

These small fish have bright orange accents on their fins and a unique pattern of white spots. They grow up to 1 inch in length and do well in heavily planted tanks. They are peaceful and can be kept in a group of at least 6 or more to feel comfortable.

Chili Rasboras

These tiny fish have a size of 0.5-0.75 inches and are peaceful, schooling fish. They require a group of at least 5 or more to feel comfortable. They are suitable for heavily planted tanks and can be kept with other small, peaceful fish.

Honey Gourami

These fish are suitable for a 5-gallon tank if kept alone. They like to hide among tall vegetation and have a peaceful temperament. They can be kept with other small, peaceful fish, but it is essential to provide enough hiding places and decorations to create a happy environment.

White Cloud Mountain Minnow

These fish are suitable for a 5-gallon tank and prefer cooler water temperatures. They are peaceful and can be kept in a small group. They do well in heavily planted tanks and can be kept with other small, peaceful fish.


A single betta fish can be kept in a 5-gallon tank, but choosing small, peaceful, and non-territorial fish as tank mates is essential to avoid aggression. Some suitable tank mates include Mystery Snails, Zebra Snails, Red Cherry Shrimp, Ghost Shrimp, Amano Shrimp, and Cory Cats.

Fish Not Suitable for a 5-Gallon Fish Tank


Goldfish can grow quite large, up to 5 inches or more, and they need plenty of space to swim around and explore. They are also big waste producers, and the water quality can quickly reach a danger zone in a small tank like this.


Angelfish can grow up to 6 inches in diameter and require a tank with at least 10 gallons of water for every fish. They also prefer taller tanks, as they can grow quite tall. A 5-gallon tank is too small to accommodate their size and provide the necessary space for them to thrive.


Most cichlids, like Oscars, Jack Dempseys, and Green Terrors, can grow quite large and require more space than a 5-gallon tank can provide. They also tend to be territorial and may be aggressive towards other fish.


While some tetras, like neon tetras, are small in size, they are schooling fish and require a group of at least 6 or more to feel comfortable. A 5-gallon tank may not provide enough space for a large enough group of tetras.

owner cleaning 5 gallon tank with magnet

Setting Up a 5-gallon Aquarium


When setting up the lighting in a 5-gallon tank, LED lights are popular for small tanks due to their energy efficiency, low heat output, and long lifespan.

Establish a day/night cycle by setting a timer for your light to ensure your fish have a consistent light schedule. This can help regulate their natural sleep/wake cycle and promote healthy behavior.

Be aware that the lighting you choose may affect the water temperature in your tank. Ensure the light does not cause the water to overheat, as this can be detrimental to the health of your fish.


Proper filtration is crucial for maintaining a healthy environment in a 5-gallon tank. Here are some tips for choosing and maintaining the right filtration system.

  • Choose the right filter: There are various filters available for 5-gallon tanks, such as hang-on-back filters, internal filters, and sponge filters.
  • Consider the flow rate: Aim for a filter with a flow rate of at least 75-100 GPH for a 5-gallon tank. This ensures that the water is properly circulated and filtered, maintaining water quality.
  • Opt for adjustable flow: Some filters offer adjustable flow rates, allowing you to customize the water flow to suit your aquatic environment.
  • Provide mechanical, chemical, and biological filtration: A good filter should provide all three types of filtration to effectively remove debris, chemicals, and waste from the water.
  • Regular maintenance: Clean the filter media and replace it as needed to ensure optimal filtration performance.
  • Monitor water quality: Regularly test the water parameters, such as ammonia, nitrite, and pH levels, to ensure the filter is effectively maintaining water quality.


When setting up a 5-gallon tank, it is essential to choose the right heater to maintain a stable water temperature. For a 5-gallon tank, a 50W heater is usually sufficient.

Small tanks have limited space, so choose a heater that is compact and easy to hide. If space is a concern, consider using an inline heater. These heaters are designed to be placed outside the tank and connected to the water intake or flow path, saving space inside the tank.

Maintenance and Care for a 5-gallon Tank

Water Changes

Regular water changes are essential for keeping your 5-gallon tank clean and maintaining a healthy environment for your fish. This helps to remove waste and prevent ammonia and nitrate levels from rising, ensuring the well-being of your aquatic pets.

Remember to monitor the frequency of water changes based on the fish density in your tank. Tank density affects how quickly waste accumulates, so adjusting the timing of water changes accordingly is crucial.

Tank Cleaning

To maintain a healthy environment for your fish, regularly clean the tank by siphoning out debris and changing a portion of the water. Remember to test the water frequently with water testing kits to ensure optimal conditions for your aquatic pets.

Regular tank cleaning is crucial for preventing a buildup of harmful substances in the water, which could jeopardize your fish’s health.

Water Testing Kits

Water testing kits are crucial for monitoring the quality of water in your 5-gallon tank. Using these kits regularly can help prevent contamination and maintain a safe environment for your fish.

populated 5 gallon tank with shell plants and fish


In conclusion, ensuring a healthy and balanced ecosystem for fish in a 5-gallon tank is crucial. Tank density plays a vital role in preserving water quality and the well-being of the fish.

Following the one-inch-per-gallon rule and considering different species’ needs, pet owners can create a suitable environment for 2-4 small fish. Prioritizing proper equipment, maintenance, and thoughtful consideration of each fish’s requirements will lead to thriving aquatic companionship.

Frequently Asked Questions

How many fish fit in a 5-gallon tank?

In a 5-gallon fish tank, you can keep a total of five inches of fish; one inch per gallon of water.

Is there a rule about how big the fish can be in my tank?

Yes, the general rule is to have 1 inch of fish per gallon of water. For bigger types, like parrotfish or large community fish—stick to just one in your 5 gallons.

Can I put different kinds of fish together in a small tank?

You should be careful mixing different types; some might not get along well. In such a small space, it’s best to pick peaceful ones that won’t fight.

What happens if I add too many fish?

Crowding too many fish in your tank will create lots of waste and could harm their health because there’s not enough clean water for each one.

Can anything other than regular kind live with my fish?

Sure! You could add snails since they’re small and don’t make as much waste as more fish would do.

If I can only have a couple of fish, how do I pick them out?

Choose ones you like but also consider size and type! Research specific needs for each kind you want—to ensure your glass tank brings joy without trouble.

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Written by Tom Cashman

I have grown up with pets for almost fifty years. My family has strong ties to the animal shelter community in Chicago. Currently I have two cats: an orange tabby named Zelda, and a gray mixed named Zander. Like all of my pets, they were adopted from a local animal shelter. Pet Zone represents my passion for sharing with the pet community.

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How Many Fish Can Safely Live In A 5 Gallon Tank?

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  1. Thanks for all this information. The kids have been after me to get them a fish tank. I think a 5-gallon would work well for them – now I know what to do!