100 Gallon Fish Tank Guide: Stocking Ideas, Setup and More…

A 100 gallon fish tank is a world of possibilities.

With a tank this size you have your own private window into an underwater world. This beautiful aquarium brings a little piece of the ocean, jungle, beach or river right into your own home.

They are a showpiece for any room and will certainly provide something wonderful to look at.

However the 100 gallon aquarium is not for every keeper. It is an expensive tank to take on and requires a lot of intensive care and maintenance.

Are you up for the task?

Keep reading to learn everything you need to know about the 100 gallon fish tank including stocking ideas, how to set up a beautiful watery world of your own and much more…

A 100 Gallon Fish Tank

100 Gallon Fish Tank Overview

A 100 gallon fish tank is usually a rectangular shape.

They are usually made from glass but you can sometimes find acrylic ones too. Acrylic are more expensive but also more durable.

With 100 gallons to work with you can keep just about any kind of marine or freshwater environment. You can even keep a paludarium that includes land and water.

All of the best and most well-loved biotopes can easily fit into a tank of this size and shape. It makes a great aquarium for a home, office, classroom or even a research lab.

If you are brand new to the art of fishkeeping then a 100 gallon fish tank is not a good starting point. The size alone means that this aquarium will require much more upkeep than smaller tabletop tanks. The aquarium itself can be quite expensive, especially when you factor in the cost of its equipment.

However for those of you with a bit of experience the 100 gallon aquarium is a fantastic choice with almost limitless potential.

Just remember though these tanks are heavy!

An empty 100 gallon tank weighs about 180 pounds. When filled with water it can weigh up to 900 pounds. Since salt water is heavier than freshwater your tank will weigh even more if it is a marine tank.

100 Gallon Fish Tank Dimension

Most 100 gallon fish tanks have dimensions of 72″ x 18″ x 20″ (L x W x H).

However the dimensions of your tank will depend on its shape and volume.

Cubic tanks are wider and deeper than long, rectangular tanks. Their width and their height are usually about the same. For example a 100 gallon cubic tank will be 50″ x 25″ x 25″. Cylindrical tanks are taller than they are wide or long so a cylindrical tank may hold dimensions of 50″ x 18″ x 35″.

What to Consider When Choosing A 100 Gallon Fish Tanks

100 Gallon Tank Coral Reef

Keeping a 100 gallon fish tank is not a decision to take lightly.

There are lots of things to consider before getting a 100 gallon aquarium.

First of all you need to consider how much space you have to dedicate to an aquarium.

You will also need to decide on the size and shape of your tank. Are you planning to keep a corner tank, or will it be the showpiece in the center of the room? On top of that you need to consider the number of fish you plan to keep. What type of habitat are you planning to keep and how many different species will you stock it with?

After you have determined the size and dimensions of your tank you can start budgeting.

A glass aquarium is the best option for a low budget 100 gallon tank. These are a good choice if this is your first time keeping a tank of this size or if you plan to keep a simple home aquarium.

When budgeting for your tank you will also need to budget for a heater, lighting system, filter and aeration as well (see our pricing advice earlier in the article).

You will then need to decide how you will stock the tank and then make sure you can afford it. When picking out your fish you need to consider what you need to support that particular species. Are they happiest alone or in a group? Will they need any specific substrate or plants to shelter in?

Finally you will need to consider the regular monthly and yearly costs of maintaining your aquarium.

The more fish you keep the higher the cost of maintaining your tank will be. Feeding and caring for a diverse habitat is not cheap. Remember even the best equipment does not last forever and you will need to replace it as it stops working. If you are using lower budget equipment this may happen more often than usual.

All of these factors must be taken into consideration if you are thinking about buying a 100 gallon fish tank.

5 Benefits Of A 100 Gallon Tank

  1. This tank size can safely host a diverse amount of species. You can keep large Cichlids, Catfish or even small sharks in this tank.
  2. An aquarium of this size provides your fish with the space that they need to keep out of one-another’s way. This is ideal for species that may not necessarily get along well in community tanks.
  3. A 100 gallon tank gives you a wider space for aquascaping. If you are a marine botanist or a coral reef enthusiast then this is the perfect tank for you.
  4. In a large habitat your fish can live and behave just as they do in the wild. Observing interactions between these species and their environment provides insight into their population dynamics that you cannot get anywhere else.
  5. A colorful and diverse aquarium is very pleasing to the eye. A large tank full of beautiful fish is very fun to watch and aquariums have been known to improve people’s mood.

How Much Does A 100 Gallon Fish Tank Cost?

100 Gallon Aquarium

This is a very expensive tank to buy and maintain.

It is not the best choice for an aquarist on a budget.

A basic 100 gallon acrylic tank can cost anywhere from $800-$1000. Glass tanks can be found for around $500 but they are less durable and harder to keep clean. If you want a package then you should expect to pay anywhere from $1200 to $1500 for an acrylic tank with a stand and a hood.

Tall cylindrical acrylic tanks are the most expensive option.

These are the types of aquariums that are commonly found in corporate offices. On average these luxury tanks cost well over $2000.

Remember too that the cost of the tank does not include the cost of equipment, stocking or maintaining the tank. Your fish, plants, coral, décor and equipment will need to be considered as well.

The equipment needed to maintain a 100 gallon fish tank will be anywhere from $500-$1000.

Stocking your tank can be expensive too. Coral reef aquariums can easily cost over $200 in corals, décor and exotic fish. Freshwater tanks are among the cheapest to decorate and find the right fish for.

But be aware that particularly fancy or exotic fish come at a high price.

100 Gallon Fish Tank Stocking Ideas

A Convict Cichlid

There are only a few fish that you cannot keep in a 100 gallon aquarium.

With a 100 gallon fish tank you have lots of room to come up with some truly creative aquascapes.

Most marine fish need larger tanks in order to be happy and healthy. You can keep most of the well-loved reef fish such as Clownfish, Wrasses, Surgeonfish, and Marine Angelfish in a tank this size.

If freshwater is more your style then you can keep almost all of the best freshwater fish in a 100 gallon aquarium.

In addition to Goldfish, this tank will accommodate Cichlids, Tetras, Rasbora, Gouramis, Danios and all kinds of Catfish. A school of Chili Rasbora would make a wonderful addition. A 100 gallon tank can even host a few of the freshwater sharks, such as the Red Tail and Rainbow Sharks.

They are also great for brackish water species. Brackish water fish are used to habitats that contain both salt and freshwater. Mollies, Gobies, Blennies, Archerfish and some Puffers are the best brackish water fish to keep in a 100 gallon fish tank.

Do not forget about some of the best non fish aquarium pets too.

The smaller Cherry, Grass and Amano Shrimp all do just fine in a tank of this size. But a 100 gallon tank can even hold a Mantis Shrimp or two. Nerite Snails and Mystery Snails make a great natural cleanup crew for your tank – they can be a big help when algae and detritus fouls up your glass or your decorations.

Coral Reef Tank

A reef aquarium is quite a conversation starter!

We recommend stocking a 100 gallon reef aquarium with hardy brain corals, mushroom corals, and leather or fan corals. An anemone or two will make one of your reef dwellers very happy: the Clownfish. Since Clownfish can be territorial you should keep them in pairs or a group of 4.

Damselfish and Royal Gramma are the Clownfish’s best tank mates. They are schooling fish so will need to be added in groups of at least 6.

You can add a Blue Tang to your reef if you want a Dory to complement your Nemo. However you can only fit one of these in a 100 gallon tank.

Finally add a few Coral Banded Shrimp to provide the perfect accent to your corals.

Goldfish Tank

100 Gallon Aquarium In An Office

This tank size is perfect for a mixed community of both Common and Fancy Goldfish.

Remember that Goldfish are a temperate water fish so do not try to mix tropical species in with them. Try keeping 2 or 3 Common Goldfish alongside a pair of Comet Goldfish. Then add a Shubunkin or a pair of Fantail Goldfish to diversify your community.

Pleco Catfish make great tank mates for your Goldfish and their spotty scale pattern really stands out against all of the gold.

For helpful live-in cleaning staff you can add up to 3 Nerite Snails to your tank. Your Goldfish will not bother these peaceful little snails.

South American Cichlid Tank

Cichlids do not always make the best community fish however if you have a large tank then they tend not to get in each other’s way.

Convict Cichlids and Green Terrors can live together so long as they are allowed to have enough space to form their territories. Try keeping a pair of each in your aquarium.

An Oscar and a Bichir make good additions to a mixed Cichlid tank. You can also include a Jack Dempsey or two in place of a pair of Convicts or a pair of Terrors.

A Pleco Catfish makes a good addition if you need a more peaceful inhabitant to balance out your rowdy Cichlids.

You can use Amazon swords and other sword plants, Java fern and floating pennywort or bladderworts.

How To Setup A 100 Gallon Fish Tank

100 Gallon Fish Tank

Once you get your new tank you will be eager to start stocking it with fish right away.

However most of your tank setup will need to be done well before your fish are added.

The first thing you will need to do is assemble your tank and fit all the equipment. This includes the filter, heater, lighting system and aeration systems.

Next you will need to clean and layer your substrate.

Run your substrate under warm water until it rinses completely clean. Make sure to lay your fine substrate first, then add your larger grains on top of that.

Once you fill your tank with water you will need to adjust the water quality. Add dechlorinators for a freshwater tank and marine salts for a saltwater tank.

Now it is time to begin cycling your tank. Some of your plants can be placed in the tank before you cycle but some may not be able to handle the shifting water quality. Check the care requirements of your plants before you add them to your tank. More delicate species should be placed after your tank is fully cycled.

Allow your tank to cycle for 6 to 8 weeks before you add your fish.

Once the cycling is complete it is time to acclimate your fish to their new home!

The floating bag method is the easiest and most common method to use. Float your fish on the surface of your tank in a bag. Replace 25% of the water in your fish’s bag with water from your tank and monitor your fish’s reaction to the water. Add one cup of water from your tank to the bag every 10 minutes or so.

After one hour of acclimation use a net to gently pass your fish from the bag to your tank. Repeat this process for each new fish that you add.

How To Maintain A 100 Gallon Aquarium

Cleaning A 100 Gallon Fish Tank

A 100 gallon tank can be a trial to maintain.

At least every 2 weeks you must perform a 25% water change and cycle your tank to balance out the amount of nitrogen.

In a freshwater tank you should dechlorinate your water every time you perform a water change. In a marine tank you will need to add marine salts to maintain your high salinity.

You must use a high power external or canister filter.

If the most efficient option is out of your budget you can fit your tank with an aquarium pump to provide some extra filtration too.

Your water parameters should be monitored every time you perform a water change. Your pH will be naturally altered by decayed plants and algae. If it is too low add a bit of distilled water to your tank. If it is too high then aeration stones can help take care of that.

Refractometers can be used for monitoring the hardness of your water and a litmus paper kit can test for low or high pH.

With a tank this size you will be busy cleaning, monitoring water quality and keeping your fish happy.

Common Problems With 100 Gallon Tanks

100 Gallon Tank

The most common mistake made with a 100 gallon aquarium is poor filtration.

Many keepers who are new to this size tank assume that a basic internal or HOB filter is enough to keep it clean. To keep the waters clean in a tank of this size you will need a high power external or canister filter. The more fish you have living in your aquarium the more powerful your filter needs to be. An aquarium pump in addition to your filter can help with cycling.

The next problem people come across is overstocking.

While a 100 gallon fish tank can hold a lot of fish, it cannot hold everything. Be aware of how many fish your tank can hold and how many of each species can be kept per gallon. Some larger fish may need over 100 gallons to be kept in pairs or groups.

Finally, some people find a tank this size difficult to keep clean.

You will need to change the water at least every 2 weeks. You can use an aquarium vacuum to clean your substrate. You may also want to add a few cleaner snails or cleaner shrimp to your community for a little extra help.

Is A 100 Gallon Tank Right For You? (Summary)

There is so much that you can do with a 100 gallon fish tank.

However you need to remember that it is a large financial commitment and requires a lot of time and energy to maintain.

If you are new to fishkeeping then a 100 gallon tank is not the best place to start. Test the waters with a nano tank or a 50 gallon tank before working up to 100 gallons.

This setup is best for those who have worked extensively with smaller aquariums and who may be ready for something a little bit larger.

Let us know in the comments section below how you are going to set up your 100 gallon fish tank…

About David Thomas

David Thomas David has been keeping fish since he was a child. In his first tank he kept goldfish and since then he has kept over 30 different species. Now he has 4 separate tanks and his favorite is a 100 gallon freshwater tank with a school of Rasboras, Tetras and Loaches.

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