12 Things Every Reefer Should Know About Reef Tank Refugiums
What Is a Refugium?
Refugiums are dedicated chambers designed to grow macroalgae as a means of filtering the water. As the macroalgae grow they will uptake nitrate and phosphate from the water effectively filtering your aquarium without the need for any special filter media or chemicals.
Easy, low-cost nutrient control is not the only benefit of a refugium either. There are a variety of additional benefits you gain from a refugium including increased pH levels and a more stable population of micro-crustaceans (pods) which bring their own set of desirable benefits to the reef.
Did You Know?
Refugiums are one of the best methods for ongoing nutrient control
They work better than filter socks, protein skimmers, and water changes combined when it comes to maintaining consistently low nitrate and phosphate levels in an aquarium. The variable rate of growth means you can maintain the exact nutrient levels you desire, no matter what kind of bioload your tank has.
Refugiums are one of the fastest ways to reduce nutrients
In addition to providing ongoing nutrient control, a refugium can effectively lower elevated nitrate and phosphate levels down to undetectable levels without costly media or chemicals.
How Refugiums Affect pH and Nutrients
The stronger the light, the better the impact on pH
Increasing the amount of light over a refugium increases the rate of photosynthesis within the algae. With more photosynthesis comes more CO2 consumption which ultimately reduces the pH-suppressing effect of excess CO2 in your aquarium. You can combat the natural pH swing that occurs in your reef tank by illuminating your refugium at night, opposite your display aquarium.
Refugiums are capable of maintaining an ultra-low nutrient environment, zero nitrates and zero phosphates
With a sufficient amount of light, a refugium is capable of removing all detectable levels of excess nutrients from the aquarium water.
A refugium with a stronger light can outcompete nuisance algae in your display
A refugium will reduce available nutrients for nuisance algae in your display and if you illuminate a refugium with a stronger light than what is over your display, you may outcompete the nuisance algae altogether. The nuisance algae will start to grow in your refugium instead of your display which is ultimately far more desirable.
Additional Benefits of a Refugium
The more PAR you provide in your refugium, the higher the pH in your display
In line with our previous observation, the more PAR you provide in your refugium the higher the pH you're going to achieve in your display thanks to the consumption of CO2 by the algae.
Algae growing in a refugium will uptake toxins
Macroalgae will uptake toxins which means these harmful toxins will bioaccumulate in the algae instead of your coral. Upon harvesting the algae and removing it from your refugium, you effectively export those toxins.
Too much growth in your refugium can benefit your corals
In a super-charged refugium with a sufficient amount of light, macroalgae can actually create too much glucose via photosynthesis and then release that extra glucose via carbohydrates directly into the water column. These carbohydrates will provide vital energy when captured by your corals.
Refugiums serve as a safe haven for microorganism reproduction
Copepods and various other beneficial microorganisms will populate and reproduce in your refugium without the pressure of predation by your fish. Pods are extremely beneficial to your aquarium ecosystem and will help to fend off nuisance algae and other photosynthetic pests like diatoms. These little critters will also increase biodiversity and support a natural food chain in your aquarium as they are suitable prey for many fish.
Things to Watch Out For
Sometimes refugiums work too well
While a refugium is capable of removing all detectable levels of nutrients from your aquarium, this is not healthy for your corals. It is best to adjust the rate of photosynthesis via the lighting to maintain a low but acceptable level of nutrients based on your typical food input. Low nutrients is the sweet spot, not zero nutrients.
Macroalgae will uptake trace and minor elements as it grows
Macroalgae will consume various trace and minor elements from the aquarium water as it grows, which also means its competing with your coral for these resources. In mature refugiums an tanks with healthy growing coral, dosing trace elements to avoid competition with your corals is recommended.
A refugium does not have to be big to be effective
In days past, it was widely believed that refugiums needed to be inconveniently large to be effective. Thanks to modern high-output LED lighting, macroalgae can grow quickly even in smaller spaces, making compact refugiums just as effective when properly maintained and harvested.
With over 25 years of experience keeping aquariums of all kinds, Robert has a detailed understanding of advanced aquarium techniques and theory. Working as a professional content creator in the saltwater aquarium industry for over 18 years, his perspective, thoughtfulness for the hobbyist, and a general understanding of the hobby, and industry that surrounds it, allows Robert to write and create digestible content that makes reefing fun and easy.
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