100 Gallon Fish Tank Guide: The Ultimate Aquarium?

The 100-gallon tank may not be the cheapest, but it’s without a doubt one of the most exciting.

This size tank helps you master all the nuances of aquascaping and the art of keeping larger fish like oscars.

Usually, people first start out with a relatively modest tank of around 10-20 gallons and then move on to more advanced tanks like a 50 gallon.

If you are ready to take a step past this, a 100-gallon tank could be for you.

Does this sounds like you, then keep on reading. We will explain everything you need to know about a 100-gallon tank and also tell you how to pick the right one.

What To Know About 100 Gallon Fish Tanks

100 Gallon Fish Tank Setup

The 100-gallon fish tank should not be considered a beginner aquarium.

This is mainly due to the size of the tank, but also because of the difficulties with handling the appropriate equipment and ensuring fish compatibility.

A 100-gallon tank generally comes in the ordinary rectangular shape. However, some of the more expensive options include cubic or curved tanks.

Regardless of the shape, your 100-gallon tank will be able to host many exotic fish and plants as well as fit many large decorations. This volume gives you the opportunity to build either a marine or a freshwater setup.

One of the biggest difficulties that an owner of a 100-gallon tank faces is choosing the right equipment – especially if you have never dealt with similar volumes.

We will cover them in more detail later on, but it is worth mentioning a little now. First, always check the output capacity of a filter when buying one. The filter will still work even if it’s not powerful enough, but it will be highly inefficient.

Although it may look like having a large tank is a lot of work, it may actually prove to be significantly easier than it seems. The conditions in such a big tank are a lot less dynamic and water tends to not get dirty as quickly.

100 Gallon Fish Tank Dimensions

The standard dimensions of a 100-gallon tank are 72½” x 18½” x 19 3/8″ (L x W x H). However, in rare cases, dimensions may be different depending on what shape tank you buy.

You might want different dimensions for a variety of reasons: optimize breeding conditions, make fish feel more comfortable or simply fit more inside. This would usually only affect the height and the width of the tank.

Fish Tank Equipment

Fish Tank Equipment

Taking care of a large fish tank can be a challenging task, but the correct equipment can make your life much easier.

Let’s take a look at the essential equipment that will help keep your tank running smoothly.


The temperature is one of the most important parts of the aquatic environment.

Many animals, not only fish, rely on temperature for survival, and severe temperature changes will affect their health.

In the aquarium, you must take care of the temperature and ensure that it stays within the allowed parameters for your fish.

These days you can pick from a range of heaters with different automation and power levels. With such a variety there should not be any problem finding the one that best suits your tank.

100 Gallon Fish Tank


The amount of oxygen and nutrients is directly linked with good water quality. Your fish depend on them to stay healthy and grow.

In the wild, water quality is regulated by a range of physical and chemical processes but in the tank, there is no water current or wind.

You must help recreate these conditions by using filters. Thankfully, filters have become an inseparable part of modern-day fishkeeping. They are widely available and easy to install, which is exactly what boosted their popularity.

With a large tank like this, you would need a powerful filter, such as a canister one with a high output. Read our complete guide here.


Never underestimate the importance of light in the aquatic world.

Light helps fish regulate their day/night cycle and helps plants get key nutrients needed for development.

Natural light can be too much for fish tanks, mainly because of excessive algae growth. So tanks need an alternative, artificial light.

Your tank will be fine with an ordinary aquarium lamp (as long as it is powerful enough). Always check what manufacturers have indicated as an optimal volume for their lamp before buying.

Other Equipment

There are also other bits and pieces of equipment that you will need.

For example, you will definitely need an aquarium stand for such a large tank.

You can also get an aquarium pump. This helps to redistribute the water in the tank more efficiently. Or you can get yourself an aquarium hood to keep the aquarium secure and regulate lighting better.

Another piece of equipment you can consider is an aquarium vacuum for substrate cleaning. Additionally, you can also get a syphon to help clean the substrate and quickly empty the tank.

What Fish Can You Keep in a 100-Gallon Tank?

Stocking Suggestions

A tank this size lets you keep many wonderful species of fish.

With so much space you can play around with it and create all sorts of unique setups and combinations.

Some of the fish you might consider include: oscar fish, gouramis (including giant gouramis), cichlids (both South African and South American), parrotfish, angelfish, rainbowfish, some larger catfish (including plecos, otocinclus catfish, and cory catfish), larger barbs, bigger tetras, and danios.

The cichlids in particular would be a wonderful choice for a community tank.

You can choose a couple of dwarf cichlid species, such as discus, Bolivian ram, and Agassiz’s dwarf cichlid. There are many other wonderful cichlids, including banded cichlids and rainbow cichlids that you can consider.

With a 100-gallon tank, you also have a wonderful choice of different saltwater fish, such as iconic surgeonfish (like blue or yellow tangs), dragonets, frogfish, some of the smaller butterflyfish, clownfish, damselfish, hawkfish, and puffers.

You may also attempt to build a miniature reef with species that include fairy and other reef wrasses, squirrelfish, and dragonets.

If you want to go with non-fish inhabitants, you can consider larger, fully aquatic crabs, Amano shrimp, ghost shrimp, and cherry shrimps as well as bigger aquatic snails, like assassin snails. They will diversify your aquarium community and will make your tank truly unique.

100-Gallon Tank Setup Ideas

Setup Ideas

There are many different setups you can have with a 100-gallon tank.

One example is a species-only tank – you could have either a school of smaller fish or a couple of fish from a larger species.

You can also consider making a community setup using only cichlids, such as discus and blue acaras.

Alternatively, you may also think about filling your tank with colorful rasboras, like harlequin rasboras or mosquito rasboras. Although they are small, several schools can fill this volume up pretty quickly.

Once you have decided on the fish, you can pick the right plants. You can also get some quality decorations as well as driftwood.

You can use rocks to make miniature crevices to give your tank a personalized touch.

Another great setup for this volume would be a reef tank. This volume offers just the right amount of space to create a flourishing reef ecosystem at home.

You can consider getting a couple of iconic marine fish, such as clownfish or angelfish. There is not much need for plants in a reef tank so you might consider getting a couple of decorations instead.

Alternatively, you can go with a community freshwater tank. This type of setup brings out all the potential of this volume, giving you an opportunity to mix and match different species and experiment with designs. You can consider getting both small and medium-sized fish for this one.

How to Setup a 100-Gallon Fish Tank

100 Gallon Aquarium

However hard it may seem to set up a 100-gallon tank, it actually just takes careful planning to ensure that everything goes smoothly. First, you will need to get all the required equipment.

This can be quite expensive but will prove to be a good investment in the long run.

Once you have all the equipment in place, it’s time to lay down the substrate (don’t forget to give it a rinse first). Depending on your fish and other inhabitants the exact substrate will vary but you will need to spread it out as evenly as possible regardless.

After that, you can start installing the equipment along with plumbing, and then start to fill the tank with water.

Depending on the type of setup you are going for (saltwater or freshwater) you may need to add different chemicals to it. Freshwater tanks will need de-chlorinator and marine tanks will need marine salt.

Once the tank is full, you can add decorations and plants and then turn on your equipment. As with all tanks, you will need to allow the tank to cycle for a minimum of 6 weeks.

This allows the nitrogen cycle to establish itself, ensuring your fish are not exposed to harmful chemicals such as ammonia and nitrites.


With a large aquarium like this, you will need to spend time making sure that all your equipment is working properly.

You will also need to clean the tank every fortnight.

Cleaning such a big tank can be quite a daunting task but thankfully there are lots of tools to help you. If you are using gravel as your primary substrate, it’s worth investing in a specialized vacuum for it. It will save you time and money.

Making frequent water renewals is important too. Keeping the water quality high is the key to keeping your fish healthy. In clean water, it would be much harder for contaminants to spread.

Aim to carry out a 20-30% water change every fortnight while you clean the gravel and wipe the algae off the glass sides too.

With the help of only several tools, as well as a consistent water renewal routine, you will have no trouble taking care of a 100-gallon aquarium.


A 100-gallon tank is a great option for experienced aquarists that want to try something new.

Just like any other large tank, a 100-gallon aquarium can host a large array of exotic marine and freshwater fish, allowing you to keep some of the most beautiful species in the world.

Getting the right equipment should not be a problem, with many models readily available at your local store.

It is not a budget option though, with tanks costing as much as $3,500.

Do you own a 100-gallon tank? If not, would you consider getting one? Let us know in the comments section below…

About Robert 454 Articles
Robert Woods is the creator of FishKeeping World, a third-generation fish keeper, and a graduate in animal welfare and behavior. He is also a proud member of the Association of Zoos and Aquariums, the Marine Aquarium Societies of North America, and the Nature Conservancy.

1 Comment

  1. Trevor says:

    I’ve had my 100 gallon for a few years now. Had a few Koi but I lost one in a move and the other one shortly after. I’ve switched to a community tank with an Angelfish and a couple albino Cory’s. I’ve recently decided to tackle a planted tank and suddenly keeping my PH up is a daily battle. I have tried API ph up. It wont hold. I’ve recently added Limestone to the tank. Hoping it helps. Next thought is Coral. Any thoughts or tips on why the sudden problem or best natural way to fix it? Thanks

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