Why Beginning Hobbyists Should Avoid Starting A Nano Aquarium

What Is A Nano Aquarium?

A nano aquarium is any aquarium that is less than 15 gallons in total water volume. ‘Nano’ is derived from the Greek nanos (νᾶνος)  meaning dwarf. 

nano aquarium

15 gallon nano aquarium maintained by an expert

To give you a rough idea as far as dimensions, a nano aquarium measuring 18″ (L) x 14″ (W) x 14″ (H) would be the equivalent of 15 gallons.

And we’ve all seen nano aquariums before at our local fish store, some even as small as 5 gallons — amazing microcosms placed on the countertop, mini aquarium lights illuminating colorful soft corals, zooanthids and perhaps a fish or two.

The fish store assistant assures us that the tiny aquarium has been running without a hitch ‘for months’, and tells us how easy and hassle free it is to maintain.

In the best case scenario, the nano aquarium you see in the store is well-tended to. The temperature is kept stable, the tank is fed sparingly and small weekly water changes are dutifully performed.

In the worst case scenario, nearly every coral placed in the tank fades and dies after 2 weeks, and they are on to their third baby percula clownfish in as many months.

There are several reasons why the beginning aquarist should not start out with a nano aquarium. And they mostly have to do with the small water volume:

  • Temperature — The small water volume of nano aquariums make them prone to temperature fluctuations. Our marine inhabitants evolved in the vast ocean where temperature is extremely stable. Depending on your geographical location a chiller, heater or chiller/heater combination will be required to keep the temperature stable in the nano aquarium, an expense to which the beginner may not be willing to commit. Relying totally on ambient temperatures to keep the aquarium temperature stable will not be sufficient. Daytime temperatures are going to be warmer with the aquarium lights on while night time temperatures are going to plummet. A temperature shift of more than 2 degrees Celsius in a 12 hour period is stressful to livestock. Any more than that would be downright dangerous, or possibly even lethal.


  • Salinity — Unless an auto top-off device is installed, aquarium salinity will rise due to evaporation. This is especially the case for  nano aquariums that are cooled by fans instead of a chiller.  Fans cool the aquarium by speeding up the evaporation process. If the aquarium is left unattended for 2 or 3 days hot days, considerable evaporation can take place. If this evaporated water is not topped up with fresh water, salinity can rise dramatically in a nano aquarium, causing undue stress for the inhabitants.


  • pH — The small volume of water in a nano aquarium makes it prone to fluctuations in pH. Dissolved organics and die-off from live rock all lead to a drop in aquarium pH, especially in a new nano tank that is only a couple of months old. Lack of regular weekly water changes and overfeeding fish can also lower pH to dangerous levels. Again this can mean undue stress or even death for the corals, invertebrates and fish through pH shock.


  • Ammonia and Nitrite — Ammonia and nitrite are lethal to fish, corals and invertebrates. And in new nano aquariums, both ammonia and nitrite can build up if regular water changes are not performed. Combine the lack of water changes with overfeeding and we have a sure-fire recipe for disaster. Bad things happen quickly in nano aquariums.


  • Overstocking — Many beginning aquarists cannot resist cramming as many corals and fish as they can into the small water volume of a nano reef aquarium. And to make matters worse, the tank is fed liberally. Everything goes seemingly well for a few days before aquarium ammonia levels rise, leading to a total tank meltdown after a week.

So what would be the smallest aquarium a beginning saltwater hobbyist could start out with?

My opinion is that if you absolutely have to start with a small tank, the minimum for the beginner would be 28 gallons.  A 28 or 30 gallon aquarium would give a slightly bigger margin of error for a beginner to make mistakes. But even a 28 gallon aquarium demands extreme dilligence with proper aquarium cycling, appropriate stocking, feeding, water quality testing and weekly water changes.

For saltwater aquariums, the bigger the volume of water, the better.

Links to more Saltwater Aquarium Setup pages:

How To Setup A Nano Tank

Aquarium Tank Size | Length, Width And Height

Ideal Location For Your Saltwater Aquarium In Your Home

Ready-Made Aquariums

Drilled Overflows Vs. Siphon Overflows

Aquarium Stands

Aquarium Chillers

Aquarium Sump



Aquarium Covers | Put A Lid On It!

Cooling Fans


What You Don’t Need For Your Saltwater Aquarium!

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