The Best 40 Gallon Fish Tanks

The 40 gallon tank, or 40 gallon breeder tank, is another one of the most common aquarium sizes available. They tend to have good dimensions and allow you to keep a much larger variety of fish within them.

However, are they actually worth it? What is so good about a 40 gallon tank and what types of fish can I house within them?

Is a 40 gallon fish tank a good tank size?

A 40 gallon tank holds a lot of water. In imperial measurements, it holds 182 litres and in American, it holds 151 litres. 40 gallon tanks usually measure about 4 ft in length, giving plenty of space for your tank inhabitants.

This space allows you to keep more varieties of fish, not just larger species, but more sensitive, specialised species and some of the more aggressive species which would normally cause issues in smaller spaces.

They are not perfect however, and their size comes with its own problems. 

40 gallon tanks are very large and very heavy, meaning it can be hard to find a place to put one, not only just for the space, but also for the safety of you and the house/building it is going in.

What do I need for a 40 gallon fish tank?

Like all successful aquariums, you will need a filtration unit; one suited to filter 180 litres of water.

For a tank of this size, in most cases, an external canister filter is the best choice. Due to the strong filtration output they offer, many people also use sump filters on tanks this size, although they are not always necessary, and all the other filter options are still usable.

You will also need a large 200 watt glass aquarium heater if you are keeping tropical fish, or even a titanium heater with a thermostat if you feel it is necessary.

A good lighting system, especially if you are growing plants or corals.

And all the other things you decide to add to your tank, decor, substrate and so on.

Should I get a 40 gallon fish tank?

Whether you should get yourself a 40 gallon fish tank or not is dependent on your situation – a better question to ask is “can you get a 40 gallon fish tank?”

Remember, the tank is around 4 ft in length and will weigh nearly 200 kilograms when filled up.

They are not ideal for upstairs apartments or small office buildings, a tank this size may be difficult to even squeeze through your front door.

If you can fit a 40 gallon tank in your home or building without any issue, then it is really down to personal choice.

We definitely recommend 40 gallon tanks due to the freedom they can offer, and the wide selection of fish they open up to you, but we recommend you to make sure you definitely can house one without incident before taking one home and causing an accident.

What to look for in a 40 gallon fish tank

40 gallons can be relatively diverse in terms of dimensions and structure, so you can find what best suits your style fairly easily.

There are “low boys” which are very flat, wide tanks with good depth and width, but little height. There are tall tanks which are the opposite of low boys, bow fronted tanks, hexagons, etc.

The top level commercial tanks available on the market today are tested and certified to be safe and resistant to cracking, collapsing or flooding.

If you are buying a custom made tank however, there are some key things to look out for:

• The first thing to look for is the thickness of glass, a 40 gallon needs to have reasonably thick glass in order to support the large volume of water.

The average height of a 40 gallon aquarium is around 50 cm, but of course this will vary. For safety, the glass should be at least 8-9mm thick, so that it can support the weight.

• The next thing to look out for are poor silicone jobs, where the glass is connected with only a very thin layer of silicone.

40 gallons is a hefty amount of water and can weigh around 180 kilograms when filled, so the silicone needs to be strong enough to hold the glass together, especially on those tall, narrow tanks which exude much more pressure onto the glass.

• Very tall tanks can be hard to perform maintenance on and can be very tricky to move. The narrow size does not provide ideal swimming space for some fish species either, like plecos and catfish which need more ground space than vertical space.

A good size tank should have plenty of depth (back to front space) to give plenty of swimming space for your fish.

• If you wish to purchase multiple 40 gallon aquariums and stack them, you will also want to look for parallel, flat sided tanks as opposed to bow fronted tanks, which can sometimes be very difficult to stack together and store.

What are the best 40 gallon tanks?

Although not nearly as common as your typical 10 and 20 gallon aquariums, a few aquarium brands will release a series of 40 gallon aquariums every few years and can sometimes be found in aquatics and pet stores.

As mentioned, the top level commercial tanks will be tested and manufactured to a professional degree and are usually very reliable aquariums.

Not all aquariums are created equally however, and sometimes a tank setup may be lacking in one particular field, such as lighting, structure or some other feature.

Through our experience in using countless professional aquariums, here are our best recommendations for 40 gallon tanks;

Aqua one horizon 182

This 4ft long tank holds 182 litres and comes with the full kit, a stand, lid, lights, filter and heater.

Juwel Rio 180 LED

A rendition of the original Rio 180 tank, but with a superior led energy saving lighting system.

The tank holds 180 litres and also comes with a cabinet, filter and heater.

Fluval Vicenza 180 LED

This 3ft tank holds 180 litres and again, comes with the full package of lights, heater and filtration unit.

How many fish can I have in a 40 gallon aquarium?

The amount of fish you keep in a 40 gallon tank really depends. Many factors can influence it, such as the species of fish, amount you feed, how strong the filtration is and how often you are willing to perform maintenance.

For most setups, you can probably keep around 20 – 30 peaceful 1”-2” long fish in a 40 gallon aquarium.

However, this number can vary greatly if we apply certain factors. For example, someone may be able to keep and breed hundreds of guppies in a 40 gallon tank, as they are small, produce only a small amount of ammonia and perhaps they do weekly water changes to keep the waste levels down.

On the other hand, someone may keep only 2 goldfish in a 40 gallon as they are large fish that need big open spaces to swim in and produce a lot of waste.

The number of fish you can keep in a 40 gallon tank will differ from person to person, but like all aquariums, you are best to not overstock a tank and try to squeeze 30 5” long fish into a 40 gallon tank.

A good way to help you better understand and calculate, go by the rule of adding 1” of fish per gallon, but keep in mind that some fish are highly territorial and may need even more space despite their small size.

Before obtaining any fish, do your research on the species you want to keep, find out how much space they need and what type of tank they are best suited for.

What is the biggest fish size you can put in a 40 gallon fish tank?

Tropical

For a tropical setup, the largest fish we would probably house in a 180 litre tank is an angelfish, they grow large, around 6” or more and can be highly territorial when they reach adulthood.

It would be best to keep just a pair of angels in a 40 gallon, as to not invite disputes and aggression issues.

Coldwater

For coldwater tanks, the largest fish we could recommend is an oranda or any of the smaller fancy goldfish.

A pair of orandas or ranchu could be kept comfortably in a 40 gallon tank, although water changes would need to be fairly frequent and good filtration would be required.

Marine

The largest fish for a marine 40 gallon tank we would recommend would be a green chromis. Although these fish are commonly seen in pet stores very small, they do actually get reasonably large when kept long enough to mature.

Green chromis typically reach sizes of around 5” in captivity and are open water swimmers, requiring a good amount of space.

A 40 gallon tank provides a decent amount of room for adult green chromis to do well in.

You could keep around 3-4 adult chromis in a tank of this size.

Best fish for a 40 gallon tank

40 Gallon tanks give you some breathing space when it comes to choosing fish you want to keep.

The extra swimming room and water volume allows you to keep some of the larger and more active species, as well as some of the more territorial fish that would otherwise cause issues in a smaller aquarium.

In this list, we will give a rundown of some of the best fish we recommend keeping in a 40 gallon tank.

All the fish in these lists will be considered in adult sizes – the fish need to be able to live in a 40 gallon tank comfortably when fully grown, not just in their juvenile state.

Tropical

Dwarf cichlids

The extra space a 40 gallon tank provides allows you to keep some of the more aggressive and territorial fish in the hobby.

Cichlids are amongst some of the most territorial of freshwater fish, but the wide space a 180 litre tank offers allows you to keep some of the smaller species of cichlids successfully.

Pseudotropheus saulosi

A small species of African cichlid that are great for those intermediate sized tanks, a group of around 4 – 5 could be kept successfully in a 40 gallon long tank.

These fish are great for more specialised community tanks, particularly those rift lake cichlid setups.

Kribensis

Another dwarf african cichlid species – these are quite a peaceful cichlid and do well in large community tanks. A pair of kribs in a 40 gallon community can be a very nice addition.

Congo tetra

A species of large african tetra, reaching about 3-4” in length. These schooling fish do best in large planted community tanks, they are peaceful and do well with other similarly sized fish.

They are easy to feed and are highly adaptable to different water parameters.

Julii corydoras

One of the larger species of Cory, these guys would pair well with the aforementioned congo tetras as they appreciate similar water parameters and live along the bottom. They make great tankmates for the lower half of your community tank.

They would be best kept in a school of around 6 – 8 in a 40 gallon tank, much like congo tetras, as they are highly social fish.

Swordtails

A species of livebearer, very similar in appearance and care to the southern platyfish, although they can reach much larger sizes, typically around 3 – 4” but some breeds can be much larger.

The males also tend to be a little more aggressive than most other livebearers however, which is why extra swimming space is needed.

Otherwise, they are peaceful towards most other community fish and are a great addition to any larger community tropical tank.

Coldwater

Small fancy goldfish

Accepting that the tank receives regular maintenance, including weekly or bi weekly water changes and has strong filtration, then it is possible to keep fancy goldfish in a 40 gallon aquarium.

However, there are only certain breeds that will be able to live in this space comfortably as adults.

Ryukens, fantails and black moors are 3 which quickly come to mind when thinking of fancy goldfish, although these fish will still grow too large for a 40 gallon tank, and are not ideal.

There are however, some smaller breeds that will suit a 40 gallon tank much better.

Ranchu

One of the smaller breeds of fancy goldfish, Ranchus can be kept in a 40 gallon tank with little issue. Even when fully grown, 2 – 3 can be housed comfortably in an aquarium of this size.

Pearlscale

Pearlscale goldfish are another one of the smallest breeds of fancy goldfish, usually reaching around 5” in size. You can get away with housing around 2 – 3 pearlscales in a 40 gallon, with regular water changes and good maintenance.

One side note to consider, is that both ranchus and pearlscales are very poor swimmers due to their body shape, and will struggle in a tank with a strong current.

Although powerful filtration is needed, you should install a filter that does not push water around the tank powerfully.

Sponge filters, hang on backs and box filters are great for fancy goldfish aquariums for this treason.

Dojo loach

The Dojo or Weather loach grows about 8” or so in length and is great for coldwater tanks. They live alongside goldfish quite well and make excellent peaceful community fish for coldwater and temperate tanks.

These fish are tolerable to a wide range of parameters, they are also easy to feed and will take dry foods readily. They will also eat frozen bloodworms, brine shrimp and snails!

Giant Danio

If you have a 40 gallon long, (a tank which is longer than 3ft) then you can house a couple of giant danios – these fish typically reach around 5” in length, much larger than their smaller cousin, the common zebra danio.

They are active and boisterous fish which is why they need plenty of swimming space, but they are fairly easy to care for. They take most available fish foods and are hardy in nature.

They do well in tanks with high water movement and high oxygen levels, so a filter with a current will usually be appreciated.

Giant danios make good tankmates for Dojo loaches, as they require similar living conditions but inhabit different spaces of the tank.

Rosy Barb

Rosy barbs are another active swimmer, they get around 5” in length and have a temperament very similar to the giant danio.

It is best to keep a school of around 4 – 6 in a 40 gallon tank as they are highly social, and they make good tankmates for other fast moving coldwater fish like danios.

They can get fin nippy however, so it is best not to keep them with long finned goldfish or slow swimmers to avoid any bullying.

Marine

Banggai cardinalfish

One of the staples of the marine hobby, cardinalfish are great for those larger sized reef tanks.

Banggais are widely available, being commonly bred in captivity these days and are one of the easiest marine fish to care for.

They will commonly take frozen food and can sometimes be adjusted to eating dry foods too!

They are peaceful community fish and are reef safe! However, mature specimens can become territorial amongst themselves, which is one of the reasons the extra space a 40 gallon tank provides is ideal.

Royal Gramma

A small brightly coloured fish, safe for reef tanks, they are another staple of the marine hobby, having a distinct fade from yellow to purple on two halves of their body.

Despite their small size of around 2” – 3”, these fish need a large tank due to their aggressive and territorial nature. They are cave dwelling fish that need plenty of rockwork and territory to defend.

A 40 gallon provides them with plenty of space to get away from other fish and live comfortably in.

As for how many to house, keep just 1 in a community tank, unless of course you aim to try and breed them, in which case they can be paired, but a larger tank may be required for this.

They are a fairly easy fish to keep, adjusting to captivity fairly well and usually taking frozen food quite easily.

Chalk Goby

Gobies are very fascinating fish to keep, they are always busy sifting through the sand and are relatively easy fish to keep.

Chalk gobies are best kept alone or in a pair in a 40 gallon tank as they can be highly territorial to one another in captivity, and need plenty of floor space from where they can dig around in.

They will often take frozen food readily and adjust to life in captivity fairly well. Just make sure that in a community tank that there is enough food which reaches the bottom, otherwise they can be outcompeted by other fish and starve.

They do well in mature reef tanks, with plenty of infusoria and tiny copepods living in the sand from which they can graze on.

They can however, spit sand on or bury corals which are sat on the substrate, so be careful if you have any corals down low. Maybe move them up onto a rock or ledge, where they will not be submerged in sand.

Valentini Puffer

A small pufferfish species ideal for a 40 gallon tank, they grow to around 4” in length and are very interesting fish to keep. 

They can adjust to frozen food quite well, but will always benefit and engage more with live foods.

They are highly predatory fish, and are not reef safe as they hunt and consume invertebrates such as shrimp, small crabs, snails and worms as part of their main diet.

As far as tankmates, they should be kept with similarly sized fast moving peaceful fish, they do well with small wrasse species, clownfish and gobies.

Ensure there is also plenty of rockwork in the tank, to provide good cover, as valentini puffers can be nippy towards other fish at times.

Valentini puffers can be kept in groups of 3 or 4, although they may need a larger space for this as they can be territorial, especially the males who will compete viciously for space, feeding rights and females.

Pufferfish are very personable creatures and can be very rewarding fish to keep either on their own or with other fish.

Best filters for 40 gallon tank

For filtration, you need a unit that is able to effectively clean a tank with a capacity of 180 litres or more. 

The filters we have picked out for this list are more than adequate for a 40 gallon tank, as we always suggest going slightly over the literage on your filter, to make sure it can definitely do the job.

These suggestions are some of the best filters we have had experience with, rated on ease of use, effectiveness, cost and overall quality.

Fluval U4

The largest of the U series internal filters, this filter contains multiple cartridges, including floss, carbon, ceramic media and sponge media.

They are highly effective at providing organic and mechanical filtration, are easy to use and are highly diverse, being able to work in a variety of different aquariums, even in large paludariums with amphibians and reptiles.

Fluval 207

This filter is an external canister, which feeds water out of the tank through a series of chambers and then back into the tank through a pipe.

Canister filters are highly effective at keeping water clarity high and maintaining sound water quality, the Fluval 207 does a great job at keeping a 40 gallon tank clean.

The filters are easy to set up and get running, the components are easy to clean and re-use and can be individually purchased as spares at most pet stores.

Hygger Double Sponge Filter – Medium

This is a heavy duty sponge filter for those larger tanks, it contains two sponge towers and two cartridges of ceramic media for bacteria colonies to grow and filter out ammonia.

It is usable in all different types of aquariums as it is air based and does not produce a current; it simply needs connecting to an air pump with airline tubing.

These filters are highly effective at biological filtration and work great for fry tanks, planted tanks, breeding setups and fish tanks which contain poor swimmers.

JUP – 02 Aquarium Filter

This internal filter comes with a built in UV steriliser as well as a sponge filter to trap debris and house beneficial bacteria.

A very effective filter usable in a variety of tanks, the filter is great for maintaining extremely clear water as the UV keeps biological waste and bacteria in the water column down to a minimum.

The steriliser is also great for disease prevention, as it will kill off pathogens present in the water.

Sump filters

For larger tanks, like 40 gallons, you may also opt to install a sump filter instead of the typical internal or canister filter.

Sump filters are typically used in very large setups, marine tanks or can be used to filter multiple tanks.

They can be easily constructed using another smaller aquarium, some glass dividers, a pump and some filter media.

The idea of a sump filter is to provide the most space possible for nitrifying and denitrifying bacteria colonies to grow by using filter media as housing.

Bio Balls

For filter media, we recommend using bio balls. They are an excellent way to provide the most surface area for bacteria, they do not clog up quickly or need regular cleaning like a sponge and do the job of breaking down ammonia and nitrites very well.

Best heater for 40 gallon tank

For a tank that holds anywhere from 150 to 200 litres, it is best to get a 200 watt glass heater, as it will cover a 40 gallon tank very well.

You could also opt for a titanium heater, especially if you have a marine tank with a sump filter that needs a strong heat output to maintain a constant stable temperature. 

Just remember that some titanium heaters will need a separate thermostat, to prevent them from cooking your tank.

For most tanks however, a 200 watt glass heater will do just fine.

For a glass heater, we can recommend the Aqua One 27.5 cm heater and the Interpet Deltatherm 200 Watt as reputable branded equipment:

For titanium heaters, we recommend the d – d 250 watt titanium heater.

Just be sure to also purchase a thermostat along with it, so that it does not overheat the tank and can be set to the right temperature.