5 Gallon Reef Tank

5 gallon reef tank with corals and urchin

Everything you need to know

Is a 5 gallon reef tank possible?

The short answer is YES! While many aquarium enthusiasts would advise against setting up a 5 gallon reef tank for beginners, setting one up is not very different from a normal sized reef tank. More regular maintenance of the reef tank and as well as more diligent observation is required with such little volume.

But how is a smaller reef tank harder than a large one?

This is a great question! Most people assume that there is more work involved with larger fish tanks. This is true in many areas such as water changes, cleanings, and equipment. However, when it comes to a 5 gallon reef tank, things get a little…weird.

Water volume

The key difference between larger reef tanks and a 5 gallon reef tank is the water volume. Higher volume means more input is required to make big changes. Alternatively, this means very little input can have big changes in a 5 gallon reef tank.

Ammonia, for example, is a dangerous compound that should always be at 0 ppm in your reef tank. If you do a big cleaning or water change in a 40 gallon reef tank and remove a lot of beneficial bacteria, you may see ammonia levels rise due to the lack of nitrifying bacteria.

In a 5 gallon reef tank, this change would happen 8x quicker.


Another key difference between a larger volume reef tank and a 5 gallon reef tank is the maintenance.

Because of how fast change can happen in a smaller reef tank, smaller and more frequent maintenance is required. While a 20% water change could be done on a 100 gallon reef tank monthly, a 5 gallon reef tank would need a smaller (5%) water change per week.

Additionally, in a 5 gallon reef tank water chemistry should be checked more often. Especially during the first few months, water chemistry must be checked multiple times a month. For example, pH and salinity can be checked every 6 days for the first three months. Once a routine and stability is established, the water can be checked monthly.

Did you know?

The worlds smallest aquarium measures just over 1 inch in height and holds a measly two teaspoons of water. Inhabited by Zebra Fish, this aquarium was created by Anatoly Konenko. Read more information here.

What can you put inside a 5 gallon reef tank?


The species on this list are ideal for 5 gallon reef tanks because they are small, do not excessively consume, and will thrive in a smaller environment.

Single fish

These fish will be ok if they are alone in a 5 gallon reef tank.

  • Yellowtail Damselfish
  • Citron Goby
  • Green Banded Goby
  • Twin Spotted Blenny
Two Fish

Two of these smaller fish are suitable for a 5 gallon reef tank.

  • Blue Neon Goby
  • Clown Goby
  • Trimma Goby
  • Redhead Goby
  • Yellow Neon Goby
  • Eviota Goby
Other Animals
  • Sexy Anenome Shrimp
  • Pom Pom Crab
  • Hermit Crab
  • Mystery Snail
  • Emerald Crab
  • Banded Coral Shrimp

Special considerations must be made when deciding what to load inside of your 5 gallon reef tank.

Biological Load

Biological load in your aquarium is the ability of the tank to process waste produced by organisms living within the tank. If there are too many organisms like fish or shrimp inside the aquarium, the bacteria will not be able to keep up with the excess waste.

What this means is that it is important to choose slow growing and small species for your 5 gallon tank. Slower growing species will produce less waste and contribute less to the biological load.

Species Compatibility

In a 5 gallon reef tank, species compatibility doesn’t quite work like it does in larger reef tanks. Species that normally would be considered compatible for a 30 gallon tank may show aggression with such limited space.

When choosing corals, a hardy and slow growing species must be chosen. Any species of coral known to grow quickly or aggressively will outpace and strangle any other life in the reef tank. This problem is a common consideration for standard sized reef tanks, but the problem is amplified for a 5 gallon reef tank. Common 5 gallon reef tank coral species include:

  • Zoanthus
  • Caulastraea spp.
  • Blastomussa spp.
  • Duncanopsammia Axifuga

How Expensive is a 5 Gallon Reef Tank?

The price to set up a 5 gallon reef is heavily dependent on the species of fish or coral you choose to put inside. A recommended practice when setting up a 5 gallon reef tank is adding corals first, after the water has cycled, and adding any fish or animals at a later date.

Startup Costs:
  • Tank: $40.00 – $60.00
  • Lighting: $40.00 – $90.00
  • Filtration: $25.00 – $130.00
  • RO Salt Water: $20.00

5 Gallon Reef Tank Startup Cost: $125.00 – $300.00

Ongoing Expenses:
  • Water Testing Kit(s): $30.00/3 months
  • RO and Salt Water: $12.00/3 months
And don’t forget the reef!

Pricing for corals and fish will depend on the selection of species made. Below is an example of how much it would cost for one of many 5 gallon reef tank options.

  • Yellowtail Damselfish: $15.00
  • Caulastrea Coral: $30.00
  • Blastomussa Coral: $55.00
  • Zoanthus Coral: $25.00

Example Reef Tank Stocking Expense: $125.00

Interested in seeing a final product?

Check out this YouTube video from ReefSpy about their 5 gallon reef tank.

How to Set up a 5 Gallon Reef Tank

To set up a 5 gallon reef tank, take the steps you would normally take to set up a reef tank. Several in-depth guides can be found on YouTube or there is a great article from LiveAquaria available here.

Note: It is important to remember the sensitivity with a 5 gallon reef tank. Minor adjustments can result in big changes. Take every guide and tutorial with a grain of salt as you may have to tweak things slightly to fit your build.

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