What To Put In a Saltwater Aquarium Refugium

what is a refugium

The aim of a saltwater aquarium is to mimic what we see in the wild, and a refugium can contribute significantly. Not only does a refugium have the potential to provide your fish with live food, called pods, but it can also play a crucial part in maintaining nutrient levels. This ensures the environment is kept content and healthy.

Pods are first introduced into a marine system with the introduction of live rock. However, they can also be introduced separately. They would have enormous potential to breed to incredible numbers in your tank were it not for the fish you keep!

By providing a refugium, big or small, you are providing a refuge or safe environment utilising the tanks water in which they can safely increase in number among the macro algae in your refugium.

Provided conditions are in their favour, which you shouldn’t have a problem with because they are a robust creature, you are providing fish like Wrasse, Dragonet Mandarin and Scooter Blenny with a plentiful supply.

What is a refugium?

A refugium is potentially a very beneficial addition to any marine tank, being multifaceted in nature. 

As well as providing a safe environment for the proliferation of copepods and amphipods, it provides a natural solution to phosphate and nitrate reduction and control in your system.

Once set up, they are easily maintained.

refugium chaeto or caulerpa

What to put in a refugium?

Refugiums are simply an area away from the main display in which you grow and harvest macro algae.

Unlike unwanted algae such as green hair algae and brown algae that you don’t want in your tank, macro algae can form an integral part of your nutrient export program by reducing nitrates and phosphates.

The most commonly used macro algae is Chaetomorpha and Caulerpa but there are others available too.  Given the correct lighting and ongoing nutrients produced by your fish they will grow incredibly well while consuming excessive nitrates and phosphates in your system.

Refugiums, also called algae beds by some, can have the ability to be used as your sole form of nutrient control depending on the levels you are trying to achieve.  They are also one of the main components of the Triton Method.

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Caulerpa vs Chaetomorpha

The two most common macro algae used in refugiums of saltwater aquariums are caulerpa and chaetomorpha, or chaeto for short.   

In my opinion, I prefer to use chaetomorpha as it has no chance of reproducing in my display tank.  Other reefers have been perfectly happy growing caulerpa in their refugiums but it’s not something I’m willing to risk.  (A quick google search for ‘How to get rid of caulerpa’ should be enough to put you off!)

Hopefully after reading the pros and cons of both caulerpa and chaetomorpha you can make an informed decision.



Caulerpa, such as racemosa (green grape), can grow almost twice as quickly as cheato within the same time period.  

It is great at exporting nitrates and phosphates. 

Tangs and other herbivores love it!  You can trim it regularly and place it in a feeding clip as you would with nori. 

Just ensure that the caulerpa you are growing is suitable for fish to eat as some can be toxic.  The general concensus however is that green grape caulerpa is okay for fish and invertebrates.


You may or may not have heard the phrase ‘my caulerpa went asexual’.
This refers to the ability of all caulerpa species, under the correct conditions, to release a multitude of spores into the water column.

This happens when the nutrients in the system drop to almost zero.  The plant will then die, and in its final act release the spores as an act of preservation.  It will also release the nitrates and phosphates that were incorporated into it’s structure.  Visually, this looks like a tank suddenly turning cloudy.

To prevent this from occuring it is recommended that your refugium lights remain on 24/7, as it has been established that the caulerpa will normally go asexual when the lights are out.

As you can imagine, the release of spores in the water has the potential to end up in your display, and to take root there.

Although this is mentioned as a pro, it can also be a con.  Caulerpas tendenency to grow quickly is not always a good thing.  If it were to go asexual and release spores into your main display tank, you will struggle to remove it.  This is because if you did manage to remove it, even a small amount left on a rock will grow rapidly to form a new clump.   

Taxifolia is known to be a particularly rampant and invasive species. 


caulerpa versus chaetomorpha
Photo kindly provided by Bob Peterson on Flikr.com



Unlike Caulerpa, chaeto does not ‘go asexual’ and release spores into the tank.

Chaeto also doesn’t need anything to grow it’s roots into.  It floats near the surface of the water, as in the photo below.  

Like caulerpa, chaeto is also great at nutrient export. 


Chaeto doesn’t grow as fast as caulerpa.

Generic Live Chaeto Chaetomorpha Macro Algae Reef Refugium Saltwater Plant Marine
  • 1/4 cup of Chaeto, Chaeto is the easiest beginner macro algae for those that are looking for macro that is hardy and does a great job with nutrient export.
  • Great source of natural nutrient export helping to reduce and absorbs nitrate and phosphate.
  • Creates a natural habitat for copepods, amphipods, and other livestock.

Refugium Lighting

This is an extremely hot topic inundated by multiple viewpoints because of huge light selection available however the two most popular are:

6500K bulbs

Macro algae is a plant.  Plants both above and below water respond to light in the 6500K range.  Your every day dining room warm white light is 6500K.  If you were to hang the same light above your chaeto or caulerpa it would grow, as long as nutrients were available to absorb. Using an 6500K LED light is cheaper again.  Using a 6500K bulb with a lamp holder suspended above your refugium will ensure you get good macro algae growth.

Kessil H80 Tuna Flora Refugium LED
  • The h80 tuna flora features four efficient spectrums - blue, grow, bloom, red - in one single
  • Fixture: The light is perfectly blended, with wavelengths including true uvand infrared
  • (Ranging from 360-780 nm), enhancing photosynthetic efficiency

Refugium specific lighting

If you want fantastic growth, look no further than purpose made refugium lights. These are based on the spectrum of grow lamps used in horticulture, and are just as powerful over a refugium.  These are LED lights comprised of a mixture of blue and red LED’s.  They are known to encourage much faster growth.

So, what is the difference between the two?

6500k light gives more natural growth but does encourage coralline growth too.

Macro algae grows faster under grow lamps such as the Kessil H80 Tuna Flora Refugium LED without encouraging coralline algae.  This is what the majority of reefers opt for as you won’t have to scrape the sides of the refugium or watch to see that the coralline algae isn’t growing to interrupt flow from the pump intake.

Coralline algae is in fact a sign that your system is doing really well.  It can be a pain however to keep off the glass and plastic components of your display tank.  If you have this issue, you may want to read this article on how to remove it.

Refugium substrate

Refugium substrate can either be the usual live sand you use in your display tank, mud, or both!  

Substrate such as live sand and mud, such as Miracle Mudis useful for growing caulerpa as it allows this macro algae to gain a foothold, keeping it anchored.  

Mud contains trace elements such as iodine, calcium, iron, strontium and free carbon which are beneficial to coral and macro algae.

Both sand and mud create a habitat for copepods, amphipods and worms, amongst others, in the refugium.  They also both contain live bacteria which contributes to a healthy ecosystem.  (Presuming of course, you are using ‘live’ sand.)

However, there is much debate over which is best, if any at all!  

Live rock and live sand in your display tank provides enough bacteria to take care of your biological filtration without the addition of mud or sand in the refugium, therefore substrate in your refugium will have little effect on the overall bacteria population.  Mud does however provide a ‘base’ ensuring that even minimal quantities of trace elements are always available.

Mud does need to be replaced every year or so as the trace elements will have been used over that period of time.  

Adding mud to an existing system can be a messy business, and should ideally be added slowly.  As you can see in the photo below, adding all the mud at once will leave you with a pretty murky tank for a day or two. The good news is all fish will be fine, and your corals unharmed.

miracle mud refugium

Nano reef refugium - Is it worth it?

Generally, refugiums are associated with sumped systems on larger saltwater aquariums.  You will probably find information online telling you that the refugium should be a certain size to deal with a given volume of water.

In my experience however, you can shove chaeto into just about any space and, with the correct lighting, you will benefit from reduced nutrients.  Provided you are not overfeeding and your tank is not overstocked.

When I started out in marine I had a nano tank with rear compartmentalised system.  I dedicated one of the four compartments to a mini refugium with a Nano-Glo Refugium Light.  The chaeto grew fantastically well and kept nitrates in particular, in check.  However the fast flow through through the compartments was unsuitable for breeding pods. 

JBJ Nano Glo LED Refugium Light for Aquarium
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If you don’t have a sump and your intention is to use a refugium aimed at breeding pods, all is not lost.  There are specialist HOB ‘Hang On Back’ refugiums made for just that purpose, with the correct light included too.

Although I have not used one myself, this CPR Aquatic AquaFuge 2 Large Hang-on Refugium comes highly recommended.  Not only will this give you an immediate solution to both macro algae use and pod breeding, but it will also increase your total water volume, which is never a bad thing.

So there you have it!

I will always run a refugium as it can only be beneficial when used with macro algae.  Although it must be said that not having one does not mean you won’t be successful in keeping a reef tank.    

I have tried miracle mud and sand on separate occasions in my saltwater aquarium’s refugium and in my opinion, I will not be using either again.  I have decided to stick to chaeto which does not require any substrate to anchor into.  I find that keeping the base bare makes it easier to siphon out detritus should it become an issue, and it invariably does from time to time.  

I am more than happy taking the time to dose trace elements should my tank fall short.  

What To Put In A Refugium?