How Many Fish Can You Keep in a 40 Gallon Aquarium?

The number of fish you can keep in a 40-gallon aquarium depends on the size and type of fish you plan to have. As a general rule, you can have about 1 inch of fish per gallon of water. Therefore, in a 40-gallon tank, you can have approximately 40 inches of fish. However, it’s important to consider the adult size of the fish and their compatibility with each other to ensure they have enough space to swim and thrive.

How Many Fish In A 40 Gallon Tank

40 Gallon Fish Tank Equipment

When it comes to a 40-gallon fish tank, maintaining the proper environment is crucial for the health and well-being of your aquatic pets. Even slight changes in temperature, chemical composition, or flow intensity can have a negative impact on the delicate balance of their ecosystem. To ensure that your tank’s conditions remain optimal, you’ll need the proper equipment. Let’s explore some essential equipment you may want to consider for your 40-gallon fish tank.

1. Filter:

When it comes to setting up a 40-gallon fish tank, one of the most crucial pieces of equipment is the filter. It plays a vital role in keeping the water aerated and creating a healthy flow for your aquatic pets throughout their lifecycle.

Choosing the right filter is an important step in recreating a natural environment for your fish. It’s necessary to consider your tank’s size to ensure it functions efficiently, as it needs to be capable of filtering all the water in the tank around 4 times per hour for optimal performance.

Additionally, understanding the specific requirements of your aquatic inhabitants is vital since different species have varying water flow preferences. Once you’ve figured out what works best for them, you can choose a filter that fits both their needs and your budget.

2. Heater:

In order to create an ideal environment for your fish, maintaining the right temperature is crucial. Failure to do so can lead to serious health complications for your aquatic friends. This is where a heater comes in – a simple yet essential piece of equipment for any 40-gallon fish tank. Connected to a power source, a heater keeps the water at a set temperature and ensures that sudden changes are avoided.

Modern heaters often have thermostats that switch off the power once the temperature has been reached or surpassed. It is crucial to invest in a reliable and efficient heater when trying to create and maintain a healthy environment for your aquatic friends.

3. Lights:

When setting up a 40-gallon fish tank, lighting is a crucial factor that should not be overlooked. Not only does it promote growth for live plants in the tank through photosynthesis, but it also plays a vital role in keeping fish and other aquatic animals healthy by providing stable daylight cycles. Inadequate light can cause health problems for your fish, while excessive light exposure can result in rampant algae growth throughout the tank. It’s important to get the lighting right to create an optimal environment for your aquatic pets.

4. Other Equipment:

When setting up a 40 gallon fish tank, it’s important to consider the necessary equipment to make it function properly. In addition to the tank itself, you may require some other helpful pieces of equipment.

An aquarium stand designed for the specific tank size is necessary. It provides enough space for organizing and storing plumbing or additional equipment, as well as maintaining stability.

In addition, it may be worthwhile to invest in smaller equipment such as gravel cleaners, magnetic sponges, or automated feeders. These items can enhance the overall quality of life within the tank and save you time by simplifying maintenance tasks.

Which Fish to Keep in a 40 Gallon Tank?

Choosing the right fish for your 40-gallon tank can be a daunting task. It’s important to keep in mind that the size of the tank will determine what types and how many fish you should keep.

When selecting fish for a 40-gallon tank, it is recommended to opt for those that are between 1-6 inches in size, ranging from small to medium.

A handy table has been provided below to help you choose which fish species would be appropriate for your tank and how many of each. This way, you can ensure that your fish have the space they need to thrive and live comfortably.

Fish NameNumberBenefits
Cichlids5 to 6 (mid-sized) and 10 to 12 (dwarf-sized)Suitable for community tanks due to their adaptive nature.
Tetras20 to 30Friendly and peaceful with most other fish species like Guppies, Mollies, Betta, and Guramis.
Mollies15 to 20Help in keeping the tank clean by feeding on algae.
Betta15 to 20Offers a beautiful appeal to the tank with its attractive features.
Guppies20 to 30Extremely friendly, low-maintenance, and love to stay in a community.
Gourami10Non-aggressive and get along with most other friendly fish species.
Cory Catfish10Known as “tank cleaners” as they help in cleaning out any leftovers.
Goldfish1Offers various benefits to humans but releases more waste as compared to other fish species.
Clownfish1Easy to care for but requires proper space.

Best Setup Ideas For a 40-Gallon Tank

When it comes to setting up a 40-gallon tank, there are certain factors you need to consider such as the temperament of different fish species. However, we understand that sometimes research can be overwhelming and time-consuming.

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That’s why we’ve compiled a list of some of the best setup ideas for your 40-gallon community tank. These ideas have been carefully selected to ensure that your fish thrive in a peaceful environment.

Setup Idea 1:

Fish SpeciesNumber
Neon Tetra5
Zebra Danio5
Dwarf Gourami1
Bristlenose Pleco1

Setup Idea 2:

Fish SpeciesNumber
Rummy Nose Tetra6
Cory Catfish5
Amano Shrimp5
Bristlenose Pleco1

Setup Idea 3:

Fish SpeciesNumber
Neon Tetra15
Bolivian Rams2
Sterbai Corys6

What Is The Biggest Fish Size You Can Put In A 40-gallon Fish Tank?

As mentioned earlier, it’s not recommended to rely solely on the one-inch-per-gallon rule for larger fish species. When it comes to determining the maximum size of fish you can keep in a 40-gallon tank, you should consider the type of fish and their individual needs.

1. Tropical:

When considering which fish to house in your 40-gallon fish tank for a tropical setup, it’s important to keep in mind the potential size of the fish as they grow. The largest fish that would be suitable for this tank size is an angelfish, which can grow up to 6 inches or more and become highly territorial when they reach maturity. To ensure peace among aquatic creatures, it is recommended to maintain a maximum of two angel fish in a tank with a 40-gallon capacity.

2. Coldwater:

When it comes to coldwater fish tanks, it’s important to consider the size of your fish. In a 40-gallon tank, the largest fish you can keep would be an oranda or any of the smaller fancy goldfish.

If you choose to keep a pair of pandas or ranch in your tank, just ensure that you do frequent water changes and have good filtration in place. This will help maintain a healthy environment for your fish. Remember, keeping your fish healthy and happy should always be your top priority!

3. Marine:

If you’re interested in keeping marine fish in a 40-gallon tank, it’s important to choose the right species that can thrive in this environment. One popular option is the green chromis, although you should be aware that they require a good amount of space to swim, as they are open water swimmers.

While these fish may start out small in pet stores, mature green Chromis can reach sizes of up to 5 inches in captivity. A 40-gallon tank is a suitable size for around 3-4 adult Chromis to comfortably live and grow. Choosing the right marine fish for your tank size will help ensure that your fish are healthy and happy in their new home.

40 Gallon Aquarium Dimensions

If you’re wondering about the dimensions of a 40 gallon aquarium, there are a few different sizes to keep in mind. The size of a standard rectangular 40 gallon aquarium is usually 36″ x 13″ x 20″, but if a longer tank is preferred, the measurements are 48″ x 12″ x 16″. On the other hand, if you opt for a breeder tank, it usually has dimensions 36″ x18″ x16″.

Keep in mind that different manufacturers may provide slightly different dimensions, so it’s always best to double-check before making any purchases. Lastly, it’s important to note that an empty 40-gallon fish tank weighs around 60 lbs, while a fully stocked one can weigh up to about 450 lbs.

What to look for in a 40 gallon fish tank

When looking for a 40-gallon fish tank, there are different options available to suit your preference. There are tanks that are wide and flat, but with little height, while others are tall with various shapes such as bow-fronted or hexagons.

It’s important to consider safety when purchasing a tank, and commercial tanks come with certifications to ensure they won’t crack, collapse, or flood. However, if you choose a custom-made tank, glass thickness is crucial in supporting such a large volume of water. For a 40-gallon aquarium, the glass should be at least 8-9mm thick.

Silicone jobs should also be inspected for quality since it holds the glass together under pressure from water weight. Keep this in mind, especially for tall and narrow tanks where more pressure is applied.

In terms of size and shape, make sure the tank has enough depth for your fish to swim comfortably. Very tall tanks can be difficult to maintain and move around. Furthermore, some fish species require more ground space than vertical space.

Lastly, if you plan on stacking multiple 40-gallon aquariums together for storage purposes, seek out parallel and flat-sided tanks instead of bow-fronted ones which may not fit easily together.

How Much Does A 40 Gallon Fish Tank Cost?

The cost of a 40 gallon fish tank will be based on the brand and material you choose. The two options for materials are glass or acrylic, each with its pros and cons. For a 40 gallon acrylic fish tank, prices start at around $200, making them the most expensive option. Acrylic is lightweight, impact-resistant, and comes in a variety of shapes, but can turn yellow and scratch easily. On the other hand, glass tanks start from around $135 and are scratch-resistant while keeping their clarity longer than acrylic. However, they are heavy and not as impact-resistant.

You also have an option to buy a kit that includes everything you need such as lighting and filters. Glass aquarium kits can start from around $200 depending on the equipment included, but keep in mind that it may limit your freedom to personalize your tank.

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If the prices seem too high for you, you can always consider purchasing a second-hand tank in good condition which may come at a big discount.

40 Gallon Fish Tank Stocking Ideas

If you’re looking to set up a 40 gallon fish tank, there are plenty of great fish species to consider. One popular choice is Gouramis, tropical freshwater fish that come in a range of colors and have a peaceful temperament. You could keep around 10 individuals in your tank, depending on the species.

Guppies are another great choice for beginners as they are social and hardy with beautiful colors, and you could keep up to 40 individuals in your 40 gallon tank. Betta fish are also very popular due to their bright colors but should be kept alone due to their territorial nature.

Zebrafish and Bamboo Shrimp are low-maintenance options that can thrive in a community tank environment. If you’re interested in setting up a marine tank, Tomato Clownfish, and Pygmy Angelfish add personality and color while being hardy enough for a 40 gallon tank size. With these options, you can create an interesting and diverse underwater ecosystem for your enjoyment.

How Much Gravel Do You Need For A 40 Gallon Fish Tank?

When setting up a 40-gallon fish tank with a standard 1″ deep substrate, you should plan on using approximately 35-40 pounds of gravel. The required amount might differ based on the tank’s size and structure, mainly if you plan to establish a more profound substrate.

It’s also essential to consider the type of gravel that’s best for both your fish and plants. Some require finer materials than others, so be sure to choose appropriately. By following these guidelines, you can ensure that your aquarium has the perfect amount of gravel for a healthy and thriving aquatic environment.

How To Set Up A 40 Gallon Fish Tank

Setting up a 40-gallon fish tank requires several steps beginning with preparing the substrate which involves washing the gravel that will be used. You should aim for about 2 inches of gravel as a substrate, making sure not to make it too deep to avoid unwanted space that may lead to the growth of anaerobic bacteria.

Installing the necessary equipment for your tank follows suit, and this includes a filter, heater, and lights. After setting up all equipment properly, you can fill your tank with water and add decorations while leaving enough swimming space for your fish.

The next step is cycling your tank which is essential in promoting the growth of beneficial bacteria in your aquarium while controlling nitrites and nitrates levels in the water. The duration of this process is between six to eight weeks, use a water testing kit along with visual observation during this period.

Remember that new fish have likely traveled long distances which will stress them on arrival, so they must be acclimatized over time before being added into their new home – this ensures a gentle transition without shocking systems into distress through sudden changes to pH or temperature.

Common Problems

Though the 40 gallon fish tank is generally problem-free, overstocking is one issue that owners may encounter. As exciting as it may be to bring home new fish, there is a limit to how many can comfortably live in the space. Even with a large tank like this, overcrowding can occur and result in territorial or aggressive behavior among the fish. It’s better to start with fewer fish and gradually add more if possible.

Another common problem lies in water changes. While it’s important to keep the tank clean, changing too much water at once (over 15%) can be harmful to the fish. Fish waste alters the water chemistry over time, so sudden shifts due to drastic water changes cause stress for the inhabitants.

Finally, under-filtering is another issue to watch out for – especially for larger tanks such as a 100 Gallon Fish Tank. Filters vary in power based on how many gallons of water they’re designed for, but owners should consider both the size and number of their fish when selecting one. A heavily stocked or large-fish tank needs a robust filter that can handle all the waste produced by its occupants.

Is a 40-Gallon Tank a Good Size?

If you are considering purchasing an aquarium, a 40-gallon tank could be a suitable choice. It is a good size, particularly if you have an interest in keeping small fish such as guppies and tetras.

Having a 40-gallon tank has many benefits, including being low maintenance and cost-effective, making it perfect for beginners. These tanks are relatively simple to maintain and clean, which means you won’t have to spend extended periods of time doing upkeep work.

Moreover, a 40-gallon tank can house more than 20 small fish species, making it an excellent choice if you want multiple types of fish living together. Even goldfish or clownfish could comfortably inhabit this tank size.

Another advantage is that they are widely available and popular among aquarium owners; hence purchasing one and the required equipment is effortless without extensive searching.

Things to Consider Before You Stock Up on Your Tank

Before you start stocking up your fish tank, there are a few things to consider. One of the most important factors is the size of the fish. You should try to house fish of similar sizes in the same tank, as larger fish may end up consuming smaller ones.

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The number of fish that you can have in your tank will also depend on their size. A 40-gallon tank has a maximum capacity for a certain number of fish, and you can use the fish calculator to determine how many you can keep based on their adult size.

As a general rule, you should have at least 2 gallons of water for every inch length of the fully grown fish. Therefore, if you have an 8-inch-long adult fish, you should only keep two such fish in your 40-gallon tank.

It’s important to remember that this calculation works best for larger-sized fish, but it can still be applied to smaller species too. By taking these factors into consideration before stocking your tank, you can help ensure that your underwater community thrives and stays healthy.

When it comes to stocking up your aquarium, there are a lot of things to consider. One important factor is the compatibility between all the fish in your tank. Before you start building your own aquarium, it’s essential that you do a little research or refer to a reliable source to understand more about the habitat of your chosen species. Some types of fish are hostile and inappropriate for a diverse society.

Betta fish and tiger barbs exhibit aggressiveness towards other compatible species hence they should not be kept together. In the case of betta fish, male ones are known to be more aggressive toward each other, so it’s best to let them stay alone. But with the right tips and solutions, even bettas can become part of a community once their stress levels are eased.

Another important thing to consider before stocking up your tank is water preparation including pH level and filtration system. Different fish species have varying needs when it comes to their living habitats. It is crucial to follow these requirements to ensure the well-being of your fish. Different types of fish have varying water requirements; for example, guppies and gouramis thrive in clean water while tiger barbs need less maintenance.

Lastly, make sure to choose an appropriate filtration system based on the size of your tank and your specific demands for keeping your aquatic life healthy!

What are the pros and cons of owning a 40-gallon fish tank?

Owning a 40-gallon fish tank can be an exciting and rewarding experience. However, like any other hobby, there are both pros and cons to consider before investing in one.


Owning a 40-gallon fish tank has its pros and cons. On the plus side, a larger viewing area adds to the enjoyment of watching your fish swim and interact with one another from afar. With big tanks like this, maintenance is easy too – cleaning and water changes are less frequent.

Having a 40-gallon size tank gives you the flexibility to choose from various fish species that require different environments, such as marine or freshwater tanks.


One of the cons of owning a 40-gallon fish tank is the initial investment required to set it up according to one’s preferences. Since it is a large tank, it requires equipment like heaters, water pumps, lights, and others with higher power capacities to function optimally. This translates to additional expenses for equipment and electricity.

Moreover, these tanks take up considerable floor space measuring about 40*20 inches in your room or office. For optimal functionality, they should also be placed away from windows or any heat-emitting devices such as ovens, refrigerators, or air conditioning units.


Is A 40 Gallon Aquarium Big?

The 40-gallon tank is comparable in size to a medium fridge. There are two types available: normal (with rectangular bottom) and breeder (with square bottom). Both can be used, but for beginners, I recommend the breeder tank.

How Often Do You Clean Your 40 Gallon Tank?

Cleaning frequency for fish tanks varies. Usually, it is recommended to clean either once or twice a week. However, this timeline can also depend on the condition of the tank.
Depending on the efficiency of your filtration system and the waste produced by your fish, a monthly cleaning schedule may suffice.

Which Kind Of Fish Cannot Live In A 40 Gal Tank?

The species identified are flower horn and oscar. While they have attributes that make them attractive, they also require a large home aquarium due to their size.
To ensure the well-being of an adult flower horn measuring approximately 12 inches in length, it is recommended to provide a minimum tank capacity of 200 gallons, with the option of going up to 375 gallons. For a 10-inch average adult Oscar fish, a tank with a capacity of 55 to 100 gallons is necessary.

How Many Guppies Can I Put In A 40-gallon Tank?

A 40-gallon tank is appropriate for housing small community fish species such as guppies. It can accommodate up to 20 guppies, but it’s recommended to maintain a ratio of 2 females to every male for peaceful coexistence.

How Many Goldfish Can Live In A 40 Gallon Tank?

Goldfish are recognized for generating a comparatively greater amount of waste than other types of fish. It is advised to keep a maximum of two goldfish in a 40-gallon tank, but a 50-gallon tank would be preferable for two goldfish.

How Often Do You Clean A 40-gallon Tank?

It is recommended to clean a 40-gallon tank at least every two weeks.

Can You Breed Fish In A 40-gallon Tank?

A tank with a capacity of 40 gallons can accommodate both small or mid-sized fish as well as a few large species for breeding purposes. This makes it an ideal tank for spawning fish.

What Is The Largest Number Of Fish Which Should Be Added To The 40-gallon Tank?

According to the article, up to thirty fish of a single species can be accommodated in the tank, including guppies and other similar breeds.


Determining how many fish can fit in a 40-gallon tank is not just about the size of the tank. Factors like the type of fish, their adult size, their behavior, and their activity level should be taken into consideration too. Overcrowding your fish tank can lead to stress, disease, and even death for your fish.

Therefore, it’s important to research and plan accordingly before adding any new fish to your aquarium. With proper care and attention, your fish will thrive in their home and bring you enjoyment for years to come.