40 Gallon Fish Tank: Everything You Need To Know

A 40 Gallon Fish Tank is a great choice for a beginner.

You can keep a wide variety of fish in this tank. It is the perfect size for your first community tank and is also brilliant for keeping singular species.

It can be quite overwhelming to learn the endless possibilities of what can be done with a tank this size.

This article talks everything you need to know about 40 gallon tanks. Including stocking ideas, running costs, common problems and much more…

A Stocked 40 Gallon Fish Tank

All About 40 Gallon Fish Tanks

Saltwater 40 Gallon Fish Tank

The 40 Gallon Fish Tank is one of the most popular beginner fish tanks.

This is because it gives you lots of stocking options, and lots of different species can thrive in this tank. It is well suited to keeping some of the most popular freshwater fish including Zebra Danios and Sparkling Gouramis.

You can house a variety of medium sized fish, with the ability to create a beautifully decorated tank with driftwood, rocks, and live plants.

However this tank is also popular among more experienced fishkeepers – it is commonly used as a breeding tank for Guppies or Oscar Fish. If you would like to challenge yourself, it is also suitable for breeding much larger species like Giant Danios and Corydoras.

You can use it for either a marine or freshwater tank.

These tanks are widely available and can be found in lots of different shapes, however the rectangular shape is most popular.

40 Gallon Aquarium Dimensions

The standard size of a rectangular 40 gallon aquarium is 36″x13″x20″.

Long 40 gallon varieties will be 48″x12″x16″.

A 40 gallon breeder tank dimensions will be 36″x18″x16″.

Just make sure to double check your specific tank though because dimensions can vary slightly depending on the manufacturer.

An empty 40 gallon fish tank will weigh around 60 lbs. Once it is fully stocked it will weigh around 450 lbs.

40 Gallon Fish Tanks Buyer’s Guide

40 Gallon Aquarium

There are many things to consider when choosing which 40 gallon tank is best for you. We have come up with several important topics to help you think over your decision.

The first thing you need to consider is why you are getting this tank.

Is this going to be a community tank or home to only one species?

Or are you planning to breed a particular fish?

This will impact the shape and size of the tank you buy. Breeding aquariums are different in shape and depth compared to a regular aquarium.

It is important to have an idea of how many types of fish you want to keep. This will let you know whether you are deciding on the right size aquarium for the species you want to keep. It is also important to consider whether the species you wish to keep require specific tank requirements and water parameters.

For example, an aggressive species may require more space than you were expecting to establish a territory.

The questions you need to ask yourself is: Is this fish best kept alone or in a group? Will I need live plants to better mimic their wild habitat? Will I need specific plants or décor for shelter?

Next you will need to consider the price of the tank and equipment.

You can expect to pay between $200-$500 for a good quality 40 gallon fish tank. Additionally, the equipment will cost anywhere up to $200. Although you may be tempted to buy the $99 starter kit, it is best to pay more for good quality equipment to save you from ongoing replacements in the future.

The long-term running costs for a freshwater aquarium will be food, power (heater, light, and filter) and maintenance products such as cleaning supplies.

To run this tank expect to pay $20-$25 per month (excluding power and specialist food).

For a saltwater aquarium the running cost will be much higher. This will include power, specialized cleaning supplies, saltwater mix, food, and water testing kits. The average monthly cost of maintaining a 40 gallon saltwater tank is $35-$40 (excluding power and specialist food).

Finally, you need to consider the equipment that is needed.

Whether you decide to have a freshwater or marine aquarium, it is more than likely that you will need a water heater. The heater size will depend on what fish you want to look after and the room temperature. The temperature difference between the required tank temperature and the room temperature tells you how many degrees your tank will need to be heated by.

For a 40 gallon aquarium you will need a heater:

  • To be heated by 9°F it will need a 100-watt heater.
  • To be heated by 18°F it will need a 150-watt heater.
  • To be heated by 27°F it will need a 300-watt heater.

How Much Does A 40 Gallon Fish Tank Cost?

The two biggest things that will impact the price of your tank are the brand and material.

You can choose between a glass or acrylic tank.

Acrylic is lightweight, has good impact resistance and comes in lots of different shapes. However it can turn yellow with age, scratches easily and is the most expensive. The price of an acrylic 40 gallon fish tank starts from around $200.

Prices for a 40 gallon glass aquarium can start from around $135.

Glass is scratch-resistant and keeps its clarity much longer than acrylic. However it is heavy and not as impact resistant.

You can also buy these tanks as part of a kit that comes with everything you need including lighting and filters etc. Obviously, the average price can change a lot depending on the equipment included but expect them to start at around $200 for glass options.

Just remember if you do buy a kit it limits how much freedom you have with personalizing your tank.

If these prices are above your budget then you can look for a second-hand tank. If you are watchful you can occasionally find like new tanks at big discounts.

40 Gallon Fish Tank Stocking Ideas


Gouramis are popular tropical freshwater fish and make the perfect addition to a 40 gallon tank.

In a tank this size you should be able to keep around 10 individuals.

Some species like the Paradise Fish and the Ceylonese Combtail are aggressive and very territorial. Whereas others like the Chocolate Gourami are very shy. Most have a peaceful temperament and add beautiful color to your tank.

Another very popular choice are Guppies. They are very popular among beginner hobbyists because they are incredibly social and hardy fish. They are also very colorful so they will brighten up any tank. You will be able to keep up to 40 individuals in a tank this size!

Betta fish, also known as Siamese fighting fish, thrive in 40 gallon tanks. They are a beautiful bright fish which come in many color variations. Just remember they are very territorial so they cannot be kept together.

Zebrafish are a popular freshwater fish species due to their low maintenance and low cost. In a 40 gallon aquarium, you can keep up to 20 peacefully. Just like Guppies they are very social fish that do well within a community tank.

Bamboo Shrimp work well too if you are looking for something a little different.

If you are going to set up a marine tank then the Tomato Clownfish is a good choice – they will add personality and color to your tank. They are a hardy species in comparison to other marine species and a 40 gallon fish tank is the perfect size for keeping them alone or within a community.

Another good option is the Pygmy Angelfish.

Setup Ideas

For first time hobbyists creating a peaceful community can be difficult.

Firstly, it is very important that the water parameters and the habitat created in the tank is suitable for all fish. For example, fish that require dense vegetation should not be in a hardscape aquarium.

Generally, a mix of shawling fish, along with scavengers and algae eating fish will make a good community. It is also best to research temperament and have a mix of fish that occupy different water levels. Another important aspect is the size of fish (especially when fully grown).

Below are a few set-up ideas that work great in a 40 gallon aquarium:

Tank Name Fish
Tetra Paradise 6-8 Conga Tetras
Bettas and Friends 1 Beta, 5 Amano Shrimp, 6 Rummy Nose Tetra, 5 Cory Catfish and 1 Bristlenose Pleco
Colorful Freshwater 4 Banded Gouramis, 8 Zebrafish, 8 Buenos Aires Tetra, 10 Panda Corys and 1 Bristlenose Pleco
Tetras and More 2 Bolivian Rams, 15 Neon Tetras and 6 Sterbai Corys

How To Set Up A 40 Gallon Fish Tank

A 40 Gallon Fish Tank

The first thing you need to do is to prepare the gravel by washing it thoroughly.

This gets rid of any dirt and dust that may be present.

You typically want around 2 inches of gravel for the substrate. If you make your gravel too deep, this will take up unwanted space in the tank and may encourage anaerobic bacteria to grow underneath where oxygen is not present.

If you decide to include live plants in your tank then you should add enough space for the roots.

Once the gravel is in place you should install all the necessary equipment for your tank. Installation will depend on the type of equipment you purchased, but it will most likely include a filter, heater, and lights.

Now you can begin to fill your tank with water.

Once the tank is full, you can begin to place the décor for your tank (remember to clean this too). Keep at least 60% of space free for your fish to swim freely.

The next process is the longest part.

This is where you need to cycle your tank.

Your tank requires a good water cycle to promote the growth of beneficial bacteria in your aquarium. This will control the level of nitrates and nitrites in the water. It is essential in making sure that the waste and old food are being broken down at a reasonable rate in relation to how quickly they are made. This process can take between 6-8 weeks to finish.

You should use a water testing kit to track this process.

Your tank is fully cycled when nitrates are being produced and ammonia and nitrite levels are 0.

You can now add your fish.

Remember, your new fish have likely travelled a long distance, so they will be stressed on arrival.

You should float your fish in your fish tank within the bag for at least 20 minutes. You should then begin to pour a cup of water from the tank into the bag every 10 minutes until full. This will help the fish acclimatize to the water conditions of the tank.

Once the bag is full you can remove the fish and release them into the aquarium.

Common Problems

The good news is there are not many problems with 40 gallon tanks.

However a problem which you may come across is overstocking.

It is an exciting time being introduced to fish keeping, you want to buy every fish you come across. However, there is a limit to how many fish you can keep in one tank. Although the 40 gallon fish tank is a large aquarium, overstocking can happen.

Having an overcrowded tank can change the temperament of your fish and they can become more territorial and aggressive.

So you should always start with the fewest fish and slowly introduce more if you can.

Another problem that can become apparent is changing too much water at a time.

You should only change around 15% of water each week.

Over time, fish waste can alter the water chemistry of the tank they are living in and during this time they will adjust to this. When too much water is changed at once, this shifts the water chemistry and can cause stress.

The last problem to be aware of is under-filtering.

Under filtering often happens with larger tanks (like a 100 Gallon Fish Tank) but it can happen with a 40 gallon tank too.

Filters are graded based on how many gallons they can turn over. However the filter you require can change depending on the size and quantity of fish you have.

A heavily stocked tank or a tank with large fish is going to need a much more powerful filter, due to the large amount of waste that is being produced.

FAQs About 40 Gallon Fish Tanks

Difference between a 40 Gallon and a 40 Gallon Breeder?

Through your journey to finding more information on 40 gallon tanks, you may come across a 40 Gallon breeder tank.

As their name suggests, these are great tanks for hobbyists whose goals are to breed fish.

These tanks are shorter and more square-shaped because they are built for a functional purpose rather than decoration. They have specific dimensions that give them a larger surface area which helps with breeding.

Should You Buy A 40 Gallon Fish Tank (Summary)

The 40 gallon fish tank makes a wonderful first time tank and it is very hard to go wrong.

Lots of beginners worry that this tank is too big for them.

However there is no problem with having a larger aquarium than needed. You can simply add plants and decoration for shy species.

This is not just a tank for beginners though, it is perfect for experienced fish keepers. You can challenge yourself with a larger, more territorial species or breeding a particular fish.

The price of these tanks are also fairly budget-friendly.

Let us know which tank you get in the comments section below…