The Best 100 Gallon Fish Tanks

You may have decided you want to go big with your aquarium and acquire a 100 gallon tank, but how do you do this, where do you get a 100 gallon tank from, are they practical and what sort of equipment will you need to power such a large aquarium?

In this article, we will provide a rundown on our thoughts about 100 gallon tanks and give some advice on how you can successfully obtain, set up and maintain one.

Is a 100 gallon fish tank a good tank size?

A 100 gallon tank is a great size for your fish; it provides them with lots of swimming room and territory.

Fish in a tank of this scale can be kept in larger numbers where they can perform natural behaviours like schooling, which they wouldn’t be able to do in a smaller tank in fewer numbers.

A large tank allows you to produce a more natural environment for your fish, and as a result they will be healthier and happier in their home.

Alternatively, a 100 gallon tank also allows you to keep some of the larger species of fish out there and some of the smaller “monster fish” like bichirs and snakeheads.

A 100 gallon tank is not without its drawbacks however, as they are extremely large and heavy (weighing close to half a tonne when filled), making them difficult to work around and find a place for in your home.

They can also be very expensive and hard to move.

What do I need for a 100 gallon fish tank?

Like any fish tank, you need a filter to maintain good water quality. For a tank this large, you will need something fairly powerful, like an external canister filter or sump filter.

Something that has a high circulation rate, anywhere from 1000 – 2000l / h will usually cover a tank of this size.

You will also need a good lighting system if you decide to keep corals or plants, and so that you can provide your fish with a proper day to night cycle.

If you plan to keep tropical fish, you will also need a good heater to bring the tank up to the appropriate temperature and maintain a stable environment.

Should I get a 100 gallon fish tank?

Whether or not you should get a 100 gallon tank is really up to you – they are a big commitment, they are hard to move and can be expensive to purchase and set up.

For some people, a 100 gallon tank is too large to even fit through their doors. Oftentimes, a tank of this size is custom made and constructed within the house or building, or is placed in before the walls are sealed.

To remove a tank of this size sometimes means to dismantle it completely, so once you purchase a 100 gallon tank, it is usually there to stay.

They can however, be very rewarding tanks and allow you to keep some of the larger and more unusual fish species, or have a graceful large planted tank full of schooling tetras or danios.

What to look for in a 100 gallon fish tank

As mentioned, most large aquariums like this are usually custom made, as they are built to fit a specific room or building.

However, there are still a good amount of pre-built 100 gallon aquariums in aquatics stores and expos that are available for purchase.

There are also many being sold or given away by people who want to get rid of them, so you may end up finding a 100 gallon tank for free if you are lucky!

Pre-built 100 gallon tanks are usually quite tall and deep, which means they need to have thick glass to support the weight and strong silicon to hold the panes together.

The height of the tank will depend on how thick the glass needs to be, but generally, most 100 gallon tanks will be around 19” to 2ft tall, so the side glass will need to be at least 12mm thick and the base glass should be at least 16mm thick, maybe a little thicker for good measure.

Thick glass like this is very heavy and very expensive to transport, so perhaps the best 100 gallon tanks to look out for are short, long tanks, like low boys, if you are looking for something on the cheaper side.

What are the best 100 gallon fish tanks?

As mentioned, 100 gallon tanks aren’t typically made in abundance like 10 and 20 gallon aquariums, as not as many people keep them.

In a lot of cases, 400 litre tanks are custom made.

However, there are some branded 400 litre tanks on the market that you may be able to find at your local fish store or have delivered to you online which are pre built.

Juwel Rio 450

The Rio 450 as you may have guessed holds 450 litres, it is close to 5ft in length and is a very large tank to house fish within.


  • Comes with filter, heater and light
  • Has energy efficient LED lighting for plant growth
  • Available in different colours
  • Great dimensions for housing larger fish


  • Comes with filter, heater and light
  • Has energy efficient LED lighting for plant growth
  • Available in different colours
  • Great dimensions for housing larger fish

Oase highline 400

A a smart and sleek designed 100 gallon aquarium setup usable in marine and freshwater tropical setups.


  • Comes with an external oase biomaster external filter, and a pre built intake
  • External filter contains a heater ideal for 413 litres
  • Comes with a good lighting system, ideal for plant growth
  • Has great dimensions for fish to swim around in
  • Has a nice designed lid with flaps to open and feed


  • needs multiple people to move and setup
  • Is very heavy
  • Intake means you have to use an external filter

How many fish can I have in a 100 gallon aquarium?

The number of fish you can house in a 100 gallon tank will greatly vary as different factors apply – some may be able to house hundreds of small tetras and rasboras that school around in the tank.

Others may house one to two large catfish or oddballs as centrepiece fish. It all depends on the types of fish, the amount of maintenance you are willing to perform, the amount that you feed and the amount of filtration.

  • All these different factors will influence the number of fish you can keep in your tank.

A good rule to go by is 1 gallon for every 1” of fish, so maybe 50 emperor tetras or guppies, but be sure to give plenty of space for them. You don’t want to cram the tank with 200 fish and then run into filtration and aggression problems.

You also don’t want to have 1 big pacu which can’t even turn around in its own tank! You still need to be careful about your fish selection, as there are still many species out there which get too large for a 100 gallon tank, despite the fact they may look small and easy to manage in the shop.

Maybe you house 4 – 5 goldfish, or maybe 2-3 bichirs around a dozen smaller schooling fish with them – just be sure they aren’t small enough to be swallowed.

It is really up to you, and what you are prepared to deal with in your tank.

Less fish means less maintenance, more fish means more work.

What is the biggest fish size you can put in a 100 gallon fish tank?


The largest fish we would recommend adding to a 100 gallon tank is a common goldfish – an adult comet can live comfortably in a 100 gallon tank.

However, remember that they need lots of open space to swim in, so a “100 gallon long” will be much better than standard cube dimensions.

Goldfish are also messy, so if you decide to house a few of them in your 100 gallon tank, be sure to keep on top of water changes and have strong filtration.

We would recommend housing no more than 5-6 adult common goldfish in your 100 gallon tank.


The largest tropical fish we would recommend to house in a 100 gallon tank would be a bichir. They typically grow to around 1.5 – 2 ft in length and need a large floorspace to swim around in.

They are bottom dwelling ambush predators and aren’t very active as far as fish go, but this is what makes them ideal for a 100 gallon tank and around 3 – 4 adults can be comfortably housed in a tank of this size.


The largest fish we would add to a 100 gallon marine tank would be a yellow tang, and this is perhaps the minimum tank size for one adult.

Yellow tangs are reef safe, they need plenty of rockwork and algae to graze on. They do well in communities but can be very territorial in captivity when kept with other tangs.

Best fish for a 100 gallon tank

100 gallon tanks provide you with a lot of variety with setups and gives you the freedom to create many different types of tanks.

The space alone allows you to keep a range of species, not just fish, but things like turtles, frogs, geckos and small lizards if you decide to set up a paludarium.

You just need to be careful with what you decide to keep and to not get too excited; although a 100 gallon tank is large, it has its limits.

This list contains some of our best picks for fish to keep in a 100 gallon aquarium comfortably, with little to no issue, even when fully grown.


Fancy goldfish

All breeds of fancy goldfish can be comfortably housed in a 100 gallon tank; even the larger ones like ryukens and tamasaba, which reach around 8” or more.

The tank provides them with enough swimming space and plenty of water which will take a long time to foul.

You can probably house around around 8 – 9 full grown fancy goldfish in a 100 gallon aquarium comfortably, although you will need strong filtration to cope with the waste output.

Common goldfish

You can also keep adult common goldfish or comets in an aquarium this large, as the open space provides them with plenty of swimming room.

We would recommend housing no more than 6 – 7 adult common goldfish in a tank this size however, as they still produce lots of waste, which can cause high ammonia, so strong filtration and regular water changes are still a must, even in a 100 gallon tank.

Rainbow shiner

A brightly coloured, active cold water fish that lives in moving rivers and streams, they grow to about 3” – 4” but like to live in large schools and are highly active.

Rainbow shiners excel in large numbers, and in a large tank they will sometimes engage in schooling behaviour which can be a joy to see. 

You could house around 20 – 30 shiners quite easily in a 100 gallon tank and may even be able to breed them effectively, as the large space will provide the males with enough territory to spawn.

Fathead minnow

Another coldwater river fish similar to the rainbow shiner, it likes similar conditions and also appreciates living in large schools.

They do well in long tanks with plenty of swimming space, strong currents and high oxygen levels.


Peacock cichlid

The open space of a 100 gallon tank provides more territory for those particularly aggressive or irritable fish too, which means you can have more types of cichlids.

A 100 gallon peacock cichlid tank can be an amazing display tank as it provides lots of movement and colour.

Peacocks are a joy to keep but it is only possible in larger tanks due to their territorial nature and size. We recommend housing around 20 in a 100 gallon aquarium with decent filtration and regular water changes.


As mentioned, bichir can be housed in a 100 gallon tank fairly comfortably and make an excellent addition to those “smaller” monster fish aquariums.

They are fairly easy to care for and are not particularly aggressive, although they will eat smaller fish.

We would recommend keeping no more than 3 adult bichirs in a 100 gallon aquarium to provide them with enough room and to keep down on the ammonia output.


As mentioned, a 100 gallon tank gives you more territory which means you can play around with more cichlids and create all different types of community tanks.

Discus are stunning fish and can be incorporated into those warmer south american tank setups. They do well with cardinal tetras and julii corydoras and look amazing in a planted tank.

You could possibly house around 10 discus in a 100 gallon tank, but be aware that as they mature, they tend to pair off and will become territorial; so make sure there is plenty of cover and line of sight blockers for them to get away from each other.


Angels are very similar to discus as they are close cousins, although angelfish can often be incorporated into a wider variety of community setups due to their hardy and adaptable nature when it comes to different water parameters.

Angelfish can be kept at cooler temperatures than discus, and are able to go down to around 24C, which means they can be housed with a much wider range of tropical species more comfortably.

At most, we would say to add 10 adult sized angelfish to a 100 gallon, but much like the aforementioned discus, as they pair off, they will become more territorial, so make sure there is plenty of cover and plantlife for them to hide amongst.

Yoyo Loach

Also known as the Pakistani loach, these fish are one of the smaller species of loach, maxing out at around 7” although they are highly social and active.

In a 100 gallon, you are given enough space to house a few of them, which is ideal as they like to stick together in large groups.

Around 15 is a good number to go with in a 100 gallon tank.

Hoplo Catfish

Hoplos are a really interesting fish to keep either in a species only tank or in a community, they get along well with most peaceful tropical fish and are a great fish for the lower level of your tank.

They are widely adaptable to a range of water parameters and are very hardy.

While hoplo cats can be housed in smaller tanks, going with a 100 gallon tank allows you to keep them in a more interesting way, as it allows you to house larger numbers and provide more floor space for them.

With this, they will be more confident and show different behaviours that they wouldn’t normally display in a smaller tank and in fewer numbers.

Much like the yoyo loach, hoplo catfish are highly social and like to stay in large groups.

Since hoplos reach around 6” when fully grown, you can house around 15 adults and maybe a couple extra in a 100 gallon.


Yellow tang

Yellow tangs can make a great showpiece fish for your 100 gallon reef tank. They are highly personable, very interesting to watch and spend all day grazing, keeping algae and pests away.

In captivity, tangs are often territorial towards one another, so in a 100 gallon aquarium, keep just 1 yellow tang per tank.

Engineer goby

These gobies grow to be a fair size if kept under the right conditions, reaching around 12” or more in some cases.

They also require lots of floor space where they can burrow and graze on infusoria, so a long 100 gallon aquarium is ideal for them.

Engineer gobies are reef safe, but like many other gobies, they will spit sand on corals which dwell on the floor, so it is best to keep your corals up high on rocks, or house them with corals which can move around, like mushrooms.

You can keep around 4 comfortably in a 100 gallon, as like all reef fish, they are territorial, but still need to be kept with others of their own species.

Copper band

Copperbands can be housed in a 100 gallon aquarium as the space provides them with enough swimming room, but also plenty of space to graze on infusoria.

Copperbands do well in old, well seasoned, “dirty” marine tanks which are full of pests like aiptasia and worms, which copperbands will feed on.

Although they can sometimes be moved onto frozen food, these fish will mainly only eat live prey, so it is important enough space is provided to allow their food sources to grow in the tank.

They are reef safe with caution, like all butterfly fish, as when hungry they will nip at soft polyps and tube worms.

Tomato clownfish

Tomato clowns are one of the larger species of clownfish, and more territorial, they can be quite aggressive when defending their home which is why plenty of space is needed.

A 100 gallon tank will be able to house a pair of tomato clowns comfortably, as they will be able to find their own space amongst the rockwork and set up shop.

Best filter for 100 gallon tank

Fluval fx6

The fx6 is an external canister filter which circulates over 2000 litres of water an hour, it holds plenty of media for biological and mechanical filtration and is very high capacity for an aquarium filter.

They are great for larger tanks, they can be linked up easily using the pipework that comes with them and are easy to disassemble and reassemble to perform maintenance.

They are an effective form of external filtration for those larger tanks, although they aren’t ideal for tanks with poor swimmers, fry or very small fish, as they may be pulled into the filter or swept up by current.

They are better for tanks with larger fish, with a heavy bioload output.

Oase biomaster thermo 600

The biomaster thermo is an external canister filter with a built in aquarium heater, they are great for larger tropical tanks and can filter a tank anywhere from 250L – 850L.

They are easy to clean and have a pre-filter chamber which can be removed without the hassle of disassembling the whole canister.

Allpondsolutions 1000EF

The 100EF external filter is great for a 100 gallon aquarium; again it is easy to set up and get running, and is fairly easy to disassemble and clean.

It is quiet running, energy efficient, and reliable.

Sump filters

Alternatively you can go for a sump filter, which would usually be custom built for your tank, they can be complex with intricate layers of filtration media and expensive equipment, or they can be relatively simple and cheap, it depends on your choice and situation.

For any sump, you need a good strong container that can hold water effectively, either a gravity fed pipe or additional pump to draw water from the tank into the filter, a strong enough pump to channel water back into the tank, and some filtration media.

As for filtration media, you have a few choices, ceramic, sponge, carbon, floss etc.

An excellent form of biological filtration is ceramic media for larger tanks as it provides the maximum possible space for beneficial bacteria to grow.

It will trap some debris but will not become clogged so does not need regular cleaning like a sponge would, the ceramic also lasts forever and does not need to be replaced once a month like floss.

Best heater for 100 gallon tank

For a tank this large, some bigger and stronger heating equipment is required. In most cases, people with tanks this large will use multiple 300w glass heaters and place them in the sump filter.

However, depending on your situation and how you want to go about heating your tank, there are a few methods.

The first and most simple method is to add multiple 300w heaters into the sump, adding 2 or more should cover 100 gallons quite easily.

We recommend the interpet 300w deltatherm heaters, they are reliable and easy to use.

Alternatively, you can use a titanium heater, and set an aquarium thermostat to the temperature you want.

Make sure that if you place the heater and thermometer in a sump, that you place the thermostat probe where the water enters the sump and place the heater where the water leaves and goes back to the tank.

This way, the water is checked on its way into the filter and heated on its way out back to the tank.

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