For many reef-keepers, a refugium is an essential part of the tank’s filtration system.
What’s a refugium? In scientific terms, a refugium is a remote ecosystem that supports a wildlife population. A reef tank refugium is based on this principle.
The idea behind a refugium is to create a specialized environment isolated from the main aquarium.
For a reef aquarium, the refugium is used to grow macroalgae. Macroalgae are marine plants that remove nutrients, like phosphate and nitrate, from the water.
Growing macroalgae in a refugium is a natural way to keep the main tank algae-free and reduce nitrate levels. As the algae in the refugium grow, they remove nutrients from the water and use them to make new tissue.
The algae must be periodically harvested as a way to remove the nutrients and keep the macroalgae actively growing.
In this article
Where Do Nutrients Come from?
Fish and invertebrate foods contain protein, fats, vitamins, and other organic substances. As your fish and LPS or SPS corals digest these foods, they release waste products into the aquarium.
This leads to a build-up of nutrients in the water, which can lead to algae problems and poor water quality.
How Do Refugiums Work?
As water from your main tank flows through the refugium, nutrients are absorbed by the macroalgae. This is how the nutrients are removed from the water.
One of the most popular and effective algae is called Chaetomorpha. Cheato is a fast grower, removes lots of nutrients, and is easy to harvest.
Halymenia sp. or Dragons Blood is another popular algae for refugiums.
Why Proper Lighting is Important
Macroalgae, like all plants, need light to survive. If your refugium has dim lighting or poor-quality lighting, the algae will just “survive.”
But you don’t want your algae to simply survive. For a refugium to work properly, the macroalgae must be actively growing and taking in nutrients.
If your refugium has poor lighting, the macroalgae won’t be able to quickly remove nutrients, and they’ll build up in the main tank. This leads to algae growth on the glass and live rock.
Lighting the Refugium
Green algae, like Chaetomorpha, thrive under the same high-intensity lighting as stony corals. The light must be bright, but there’s more to it.
Some reef aquarists use a bright daylight fixture. But experience shows you can grow lots of macroalgae with specialty LED fixtures designed for refugiums.
These lights provide mostly red and blue light, which are what the algae need for rapid growth.
The lights won’t make the refugium look natural, like a full spectrum light fixture. It will appear mostly red. But this is not important because a refugium is designed to remove nutrients, not look natural.
Refugium Lighting FAQs
What Size Light Do I Need?
The size and output of the light used depend on the size of your refugium.
Some refugiums are smaller than the main aquarium. Other reefers use a refugium that is as large as their main reef tank. Check the manufacturer’s recommendations and specifications.
You want the light to fully penetrate the depth of the refugium. Some light fixtures have adjustable output settings so you can increase or decrease the power of the light.
How Long Do I Leave the Light On?
There are many philosophies about how long to leave the light on.
Some aquarists leave the light on 24/7. Others operate the light on the same schedule as the main aquarium.
Beginning with the same on/off cycle as the main tank is a good starting point.
Some aquarists like to use the “reverse photoperiod” method. When the main aquarium’s lights are off, the refugium’s lights are on.
How Should I Position the Light Over the Refugium?
The light fixture should be positioned so the entire refugium is well lit. This will involve raising or lowering the fixture.
Some LED lights come with gooseneck mounting systems that attach to the side of the refugium.
You may want to suspend the light above the refugium, just like the lights over the main tank.
How Often Should I Harvest the Algae?
Harvesting involves trimming off and removing a portion of the algae from the refugium. This is how nutrients are physically removed from the tank’s ecosystem.
Chaetomorpha, for example, will grow into a dense mat. This makes it hard for water and light to reach the inner portions of the algae mass.
The idea is to trim away just enough algae to allow water and light to reach most of the algae. This keeps the algae in “growth mode” so it can strip out nutrients as it makes new tissue.
Experiment and see what harvest schedule keeps the algae thriving and nutrient levels low.
Top Light Fixtures for Refugiums
There are many styles and sizes of light fixtures to choose from. Not all lights have the same output and features.
We’ve selected the most popular light fixture brands and broken down the features and benefits of each one.
1. AI Prime Fuge
Aqua Illumination’s AI Prime reef lights are well respected by reef aquarists.
AI’s new Prime Fuge LED fixture uses the same high-quality LEDS but customizes the spectrum specifically for growing macroalge in a refugium.
The LED array includes PhytoRed, Red Cool white, and UV output to drive photosynthesis. The focusing lens features smooth color blending and an 80-degree spread.
The AI Prime Fuge weighs just under 1 pound and can be suspended above the refugium or mounted using the flex arm or tank mount system. Like other AI fixtures, you can use one or more over your refugium.
This smart light can be programmed using the myAI app.
2. Kessil A360x Refugium
The Kessil A360X LED is a 90-watt fixture purpose-built for use on a refugium. The fixture has a low profile yet makes 25% more light output than other fixtures in the Kessil line-up.
The standard 130-degree focusing lens may be too wide for a small refugium. Fortunately, Kessil provides a narrow 55-degree light focusing lens, making it ideal for use over a smaller fuge.
The A360x Refugium uses the latest Kessil patented Dense Matrix LED array with a specially designed reflector system.
This fixture uses Kessil Logic™ color blending technology that allows precise color blending. Kessel Logic™ uses two independent adjustment knobs. One knob adjusts the color spectrum, and a second knob is used to control intensity.
Kessil Logic™ allows for easier adjustment of the lighting system using just two knobs.
You’ll be able to select and fine-tune the light spectrum because Kessil Logic™ allows each color channel to be independently tuned to create the best color spectrum to stimulate macroalgae growth.
The smaller size makes the A360x suitable for a smaller refugium or for mounting inside the aquarium cabinet.
3. Kessil H80 tuna flora
Incorporating many of the same high-quality components of the A360x, the H80 tuna flora is less powerful and smaller in size. This makes it perfect for a nano refugium.
The silent operation and slim profile make it easy to mount over the refugium. Kessil’s gooseneck and other mounting systems are easily adaptable for use on this model and the A360x Refugium fixture.
The H80’s Dense Matrix LED array provides adjustable power output and the spectrum required to raise fast-growing macroalge.
4. JBJ Nano Glo
The NANO-GLO LED fixture was specifically designed for the 28-gallon Nano Cube CF QUAD aquarium. But the mounting system and small size make it perfect for other tiny nano refugiums.
The fixture has four 1-watt 6500 K LEDs mounted in a plastic housing.
The suction cup mounting system makes it easy to install over a small refugium. You may even be able to mount this LED fixture inside your AIO tank’s canopy.
5. Tunze LED Eco Chic refugium
The German-designed Eco Chic LED light is designed to be suspended over a small refugium.
The fixture uses a mixture of LEDs to provide red and blue wavelengths for marine algae growth.
Its water-proof IP 68-rated design allows you to submerge the fixture underwater. Tunze claims mounting the light underwater prevents light reflections on the water surface, making the Eco Chic refugium light even more efficient.
The light is typically submerged to about .5 inches. The 12-inch light is mounted to the side of the refugium with the two-piece Magnet Holder.
The Eco Chic runs on low voltage, so there is no danger when the light gets wet or is submerged.
The built-in overheating protection automatically reduces the light’s out from 10 watts to 7 watts if the temperature reaches approximately 77°F (25°C).
6. Innovative Marine ChaetoMax
This slim fixture is designed to be attached to an under-tank refugium or the side of an AIO refugium-filter system.
You can clip it to the rim of the refugium or use Velcro to attach it against the side of the AIO filter.
The light fixture uses blue, violet, magenta, and red LEDs. The manufacturer says this eliminates the need for other color LEDs and reduces energy costs to run the light.
The ChaetoMax is available in 9 and 18-watt versions. The 9-watt version measures 6.7″ x 1.85″ x 0.39”.
The 18-watt version is double the width of the 9-watt unit. The light uses low voltage and won’t add heat to your reef tank.
You can add a timer to automatically turn the light on and off.
With so many sizes of refugium lights, it may seem hard to choose one for your reef tank. While some lights seem to say they’re special chaeto lights, the fact is any marine algae will grow with them.
The main consideration is the size and type of refugium you’re running. If you have a small nano refugium or AIO filter system, the Innovative Marine Chaetomax will work nicely.
The versatile mounting system makes it easy to put the light right where it needs to be. The slim design fits just about anywhere.
Once you move for a stand-alone refugium system, you’ll need to select a refugium light that distributes the right amount of light across the surface of the refugium.
For most refugiums, the AI Prime Fuge is going to provide the right quality and quantity of light for chaeto and other species of algae that are used in refugiums.
It’s important to remember that light drives the algae to take up nutrients and grow. Skimping on a refugium light will only result in slow algae growth and nutrient build-up in your reef aquarium.
If you have questions or comments, please leave them below.