A Guide to Nano Saltwater Aquariums

nano saltwater aquarium fish

Whether you just want to keep fish and/or coral, nano saltwater aquariums can be a great starting point, particularly if you’ve never run a saltwater tank before.  Nano generally refers to aquariums that are 40 gallons and under.  You will gain a huge amount of knowledge and experience when starting off with a nano aquarium. By the time you upgrade, and you almost certainly will, you will know the basics of how to keep parameters as stable as possible and support sea life.  Keeping a larger saltwater aquarium can be daunting but a nano tank will give you a great foundation if you decide to keep a larger tank in the future.

I myself started off with a 25 gallon aquarium and it wasn’t long before I was bitten by the saltwater bug and upgraded to a Red Sea Reefer 350.  Some years later, and I now have a Reefer 625XXL and couldn’t be happier.  I’m glad I started off with a smaller tank due to the knowledge I gained and the mistakes I learned from.  Not only that but it was certainly cheaper than starting off with a large aquarium and if I found I didn’t have the time to devote to the nano tank then it wouldn’t have been a huge loss financially.

Coralife LED BioCube Aquarium Fish Tank Kit, 16 Gallon
  • EVERYTHING YOU NEED - Feature a compact and customizable filtration chamber that is already built-in to the back of the aquarium – easy to setup and maintain.
  • GREAT FEATURES – Includes quiet submersible pump, dual intakes and adjustable return nozzle. Compatible with all existing BioCube accessories. Fish, corals, substrate and décor are sold separately.
  • SLEEK and MODERN – Biocubes feature a rounded edge design and is the perfect innovative all-inclusive aquarium for all needs..

Biggest differences between a nano saltwater aquariums and large aquariums

  • Possibly the most obvious, nano saltwater aquariums are substantially smaller and cheaper to purchase than their larger counterparts.  

  • Nano aquariums, such as the Coralife LED Biocube, due to their small size, require more frequent maintenance as fluctuations are more keenly felt.

  • You will be limited to what fish, coral and invertebrates you will be able to put in your tank.

  • Nano tanks are more affordable than larger aquariums.  Not only are nano tanks themselves less expensive but you can only fit so many fish and coral into such a small space therefore forcing you to spend less.  

Tips before buying:

Here are a few things to consider before buying nano saltwater aquariums:

nano saltwater aquarium

Tank location 

Where will your nano tank be situated?  It should be easily accessible and not placed in direct sunlight.  Ensure that you have a plug socket nearby as this will avoid the need for unsightly extension cables.


If you are planning on keeping your nano tank on a table, or if you are using a cabinet, make sure the table can withstand the weight of the aquarium full of water.  


Tank cycling

Tank cycling takes time so make sure you have patience!  Just because the tank is small, it doesn’t mean that it doesn’t need the same amount of time to cycle.  All saltwater tanks need time to cycle and this is usually around 4 – 6 weeks however you can help the process along by using MicroBacter Start XLM.  This introduces live bacteria which helps reduce ammonia and nitrite levels that are toxic to fish.  You will need to use your test kits to determine the right time to start adding fish.

Stocking your nano aquarium

With nano saltwater aquariums you need to be especially mindful of the type of livestock you wish to keep.  You cannot keep fish such as tangs in a small nano tank as they will all too quickly need more room to grow.  (See more on suitable nano tank inhabitants below.)  Fish should also be added over a period of time.  Doing so will not overwhelm the filtration system and cause a spike in ammonia and nitrites.  

What nano saltwater aquariums to choose?

Of course the decision will be all yours depending on what you would like to put inside the tank and how much space you have.  I would highly recommend purchasing a All-in-One (AIO) tank that has as many features included as possible, like the Fluval Sea Evo XII.     

As with anything, always buy the best you can afford.  You will never regret buying quality items, but you may just regret buying cheap ones.

Necessary extras

Most nano tanks should come with these included but if not, make sure you have:

  • Heater

  • Lighting

  • Powerhead (or similar) for water movement

  • Filter media 

  • Lid to prevent fish jumping (clowns, algae blennies, gobies and many others have been known to jump)

GankPike 8-Gallon Curved Corner Glass Saltwater Aquarium Rimless Low Iron Glass Aquarium Marine Fish Tank Reef Tank with Lid, Protein Skimmer, LED Light and Pump
  • 🐠 8 gallon curverd cornor design ultra clear crystal glass aquarium for saltwater fish, reef and coral. 1.5 gallon back filtration area plus 6.5 gallon front viewing area. L: 13.8 x W: 11.8 x H: 11.8 inches.
  • 🐠 Equipped with biochemical & mechanical filter media, adjustable pump and protein skimmer to keep your tank clean and provide a perfect environment for fish, reef and coral.
  • 🐠 The tank features an aluminum alloy LED light to highlight your fish, reef and coral. The LED light has 3 color modes, 5 level dimmable and auto-off timer, which helps the coral grow.

The following will not usually be included so you may need to purchase: 

  • Test kits (ammonia, nitrites, nitrates)

  • Thermometer

  • Aquarium sea salt (if you are making your own salt water)

  • Refractometer

Not necessary but 'great to have' extras

Items that are not absolutely necessary but great to have: 

  • Auto top off unit such as this one  

  • Protein skimmer – see our page on Nano skimmer options here

  • Refugium

  • Separate filter chambers

  • Controller

Tank Inhabitants

So, what can you keep in a nano saltwater aquarium?  Here are a few suggestions: 


  • Clownfish 

  • Blennies – Scooter blennies are not recommended for beginners*

  • Cardinalfish

  • Blue-Green Chromis

  • Gobies – Mandarin dragonets are not recommended for beginners however neon gobies a good option.

  • Royal gramma

  • Blackcap basslet

  • Damselfish – Some can be aggressive but the Sapphire Damselfish is a good choice.

*Mandarin dragonets and scooter blennies need a constant supply of live copepod in order to survive.  This is the main reason they are better off for those who have mastered the fundamentals of running a saltwater aquarium.

nano reef clownfish
saltwater nano fish
exotic nano reef fish

Just starting out in the hobby?
Get your copy of How To Set Up A Successful Saltwater Aquarium ebook today.

This ebook will help to guide you past the mistakes I have made over the years.


  • Cleaner shrimp

  • Sexy shrimp (also known as Anemone shrimp)

  • Hermit crabs

  • Snails

nano marine inverts


  • Zoanthids (or zoa for short)

  • Mushrooms – such as Rhodactis

  • Pineapple coral

  • Clove polyp

  • Green star polyp

  • Candy cane

  • Pulsing xenia – however these grow and multiply rapidly

Choosing coral is another fun part of owning any saltwater tank but you will also need to think carefully about how quickly a coral will grow.  Your tank may be overrun by one particular coral with no space for more.  Some coral can be aggressive and sting others that encroach on it’s territory.  Do not pack coral in too close to each other so they have enough room to grow and will have enough access to lighting without being overshadowed by another coral. 

nano coral reef tank
best corals for nano reef

Nano saltwater aqauriums need-to-knows

As a first time saltwater aquarium keeper, here are some important things to take into consideration: 


Because nano saltwater aquariums are that much smaller, their fluctuations will be noticeably larger than that of a bigger tank.  Saltwater systems rely on stability.  This means that any changes you make need to be done slowly.  Anything from raising or lowering salinity, lighting levels or water changes, should all be done in small increments.


Tap water is not good enough for keeping saltwater fish in.  Using tap water will create all sorts of problems, not least algae blooms.  You will need RO water (see this article for more information).  You can make this at home using a filtration unit attached to your home’s water supply or you can buy it directly from your local fish shop (lfs).  When starting off, the latter may be a better idea until you’ve established that you want to carry on with a saltwater aquarium.  After that, you may want to invest in an RO unit.

Water testing:

You will need to have test kits in order to keep an eye on your nano aquarium’s parameters.  Test kits for phosphates, nitrates and alkalinity will be the main test kits you will need to start off with.  You can get your tank’s water tested at your local fish shop, buy a water test kit online (which you then have to send off in the post) but having your own test kits is much easier as you can retest the water’s parameters once you make any changes. 

Water movement:

Water movement is critical to all saltwater aquarium life.  Not only does it create flow that keep fish healthy through exercise but it circulates food and food particles, especially important when keeping coral and invertebrates.  Waste is moved about where it eventually finds it’s way into the filtration system.  You will not need anything as powerful as a gyre but a powerhead or two will do the trick. 


Water lost through evaporation must be replaced with RO water and NOT SALT WATER.  As water is lost, the salt in the aquarium becomes more concentrated so you only need to replace the RO water that has evaporated.  You can make a small mark with a marker or a piece of tape where the tank’s water level should be.  Once it drops below that line, you can then add RO water to top it off.  

Filtration media:

Filtration media such as sponges and filter wool needs be cleaned regularly, more so than in larger aquariums.  If detritus is allowed to remain in the filter media, it will cause an increase in ammonia and nitrates which is toxic to fish, as well as encourage unwanted algae growth.


A big mistake that beginner nano saltwater aquarium owners make is to overfeed their fish.  Overfeeding only adds to the bioload of the tank and can end up causing unsightly, hard-to-get-rid-of algae.  It is recommended that you feed your fish small amounts twice a day.  Fish and invertebrates are constantly on the lookout for food which is why feeding smaller amounts twice a day is better than a large amount only once a day. You can read more about what to feed saltwater fish here


If using sand, one of the most popular is Caribsea.  Cured live rock (more on that here) should be added before sand however, as this creates a more stable structure.  If placed directly onto sand, the rocks can end up shifting due to the movement of sand underneath.  

Feeding coral:  

It should not be necessary to feed coral in such a small tank as the environment is small enough for food to pass them easily.  However, if you do, the same as feeding fish applies, do not overfeed.  

Tank maintenance:

Water changes should be done roughly once a week along with regular tank maintenance such as cleaning filters etc.  Water changes should be 10 – 20% of the tank’s volume.  This keeps your system stable with no increased levels of nitrates and reintroduces nutrients back into your aquarium.  

Carbon should be replaced monthly and filters cleaned regularly, depending on how dirty they get.  


Hopefully you’ve found the above information on nano saltwater aquariums useful.  I’ve tried to make it as beginner friendly as possible but if you have any other questions then please send us a message or leave a comment below and we’ll get back to you as soon as we can. 

Hi, my name is Craig.
I am the owner of The Salty Side.
Firstly, thank you for visiting us. If you have found this article to be informative, and you now have a better understanding of the topic, then my job is done.

If you are feeling charitable, and feel I deserve a little thank you, I thank you in advance for any support given.

Nano Saltwater Aquariums – A Beginners Guide