How to Set Up a Refugium: Harvesting Macroalgae To Control Nitrate and Phosphate

In biological terms, a refugium is a remote location that protects and supports a wildlife population. A reef refugium is based on this principle and works specifically to benefit your reef tank. The idea behind a reef tank refugium is to provide an isolated environment, separate from the main aquarium for the cultivation of macroalgae, live foods and biological denitrification.

Here’s how it works; macroalgae removes phosphate and nitrate, lowering harmful nutrient levels. Pieces of rock rubble provide a place for macroalgae to attach. The bacteria in the rubble will remove nitrate through natural denitrification. Refugiums also act as a live food nursery for amphipods, copepods and other microorganisms that corals and fish love to eat.

In the early days of reef keeping, many aquarists thought a refugium had to be at least as large as the main aquarium to be effective. These monster refugiums were 100% Do it yourself, requiring drilling through glass and plumbing skills. And also, they took up a ton of space!

Today we’re fortunate to have ready-made refugiums specially designed for reef aquariums. There’s in-tank, hang-on and integrated sump solutions for placement under your tank.

The first step on your road to refugium greatness is decide what type is suitable for your tank. The CPR CITR 2 In-Tank Refugium needs no water pump. The flow-through acrylic design attaches inside the aquarium or sump, with suction cups. All you do is add a light, macroalgae, rubble, maybe some sand…and you’ve got a refugium!

The Eshopps CUBE Nano Refugium has a chamber for algae and rock but can also house a protein skimmer. Just connect it to the main aquarium, add a return pump and a small LED light.

If you’ve got the room, a Trigger Systems sump integrates a refugium area and provides plenty of additional room for a protein skimmer, filter socks and other equipment. This is a true all-in-one under-the-tank solution.

Some AIO reef aquariums have room in the filter compartments to create a drop-in refugium. Rubble and macroalgae can be used instead of filter sponges.You can also consider a hang-on refugium such as the AquaMaxx HOB-R. The AquaMaxx HOB-R is an excellent choice for existing aquariums that have no additional room for equipment under the tank. The unit hangs securely off the back or side of your aquarium and includes a small pump to move water through the refugium.

Once you sorted out the type of refugium, its time to stock it and watch it grow!

First and most importantly, choose the right macro-algae. Many reefers have great success with Chaetomorpha algae. It’s a fast grower, removes nutrients, is easy to harvest and provides a perfect habitat for micro fauna to grow and reproduce. Halymenia or Dragons Breath algae are also top performers that grows fast and will do great inside a refugium. Caulerpa is another very common refugium inhabitant but, though it's very popular, it comes with some risks.

Photo Credit: Earth.com

Caulerpa is very prolific and hardy, which is great for a refugiums, but this also means it can easily choke out competing algae for light and space. Caulerpa can also send spores throughout your display and when it dies in the process of sending spores out, the absorbed nutrients and toxins are released into your aquarium water. Many hobbyists will refer to this as “going sexual” because it is a natural reproductive mechanism. The result can be a massive infiltration of very resilient Caulerpa in your display aquarium that can choke out your corals for real estate. The released nutrients and toxins will also reduce the water quality and possibly irritate corals.

In the wild, Caulerpa is known to produce and release toxins that ward off herbivorous predators of the algae. In our aquariums, these toxins have been credited with causing problems within corals, specifically SPS corals. Furthermore, many of the corals we keep would never naturally occur in the same area as Caulerpa species, so why would we expect them to thrive together in our aquarium? The lesson here is be cautious of Caulerpa.

Macroalgae needs light to grow. In-tank and Hang on refugiums usually receive enough light from the main aquarium light but you can also very easily attach a small clip-on LED or striplight.

Refugiums located remotely or under the tank, however, will need a light source. A basic full spectrum LED fixture is perfect for this application and we stock of number of excellent options and you can also find a number of DIY plans online. The truth is that any full spectrum light source will grow macro-algae but some lights are certainly better than others.

The spectrum of light being used for refugiums has been a hot topic as of late because science has proven that particular color spectrums will promote a higher rate of photosynthesis within macro-algae. Therefore, more and more companies are releasing LED lights with a heavy red and blue color spectrums for maximum algae growth. The new Aqua Illumination Fuge light is a PRIME example and has certainly helped boost the rate of growth in our own refugiums here at Marine Depot.

Photo Credit: Melev's Reef

An advanced fuge technique is to illuminate the refugium opposite the lighting schedule of the display tank. The idea is to balance the effect of oxygen production and CO2 removal. During the nighttime, photosynthesis stops inside your aquarium and the corals will no longer uptake CO2. This leaves an increased amount of CO2 dissolved in your aquarium water which then lowers your pH level. By running your refugium at night, the algae inside the refugium will continue to uptake CO2 and help reduce the natural pH swing inside your tank that occurs each night.  This results in a much more stable pH level, keeping your corals happy.

As macroalgae grows, it’s important to periodically harvest a portion by removing it from the refugium. Nutrients stored in the algae cells can leak out, especially if the algae starts to die back. Harvesting ensures that nutrients are completely removed from the aquarium. This also opens up space for new macro-algae to grow and to continue absorbing undesirable nutrients. A very common practice when harvesting macro-algae from a refugium is to take the removed clump of algae and shake it gently in the aquarium water. This will release the pods and other beneficial organisms back into the refugium or directly into your display for your fish to feast upon.

ReefPODS Tisbe are our most popular live food from AlgaGen.

Seeding your refugium with copepods is an excellent practice and highly recommended, especially with newly established aquariums that may not already have established a stable population of pods.

Using Miracle Mud or Fiji Mud as a substrate in the refugium has some additional benefits as well but is certainly not required to reap the benefits of a refugium. Personally, I do not use substrate in a refugium for the simple sake of keeping things clean. Typically, I will use just a few pieces of rubble rock with a large clump of chaetomorpha. Generally speaking the flow rate through a refugium is fairly slow, you really don’t want to be rushing water through it because this can disturb some of the beneficial processes going on inside your refugium. High flow will also spread substrate or bits of algae throughout your display.

Setting up a refugium has never been easier and the benefits are real. No matter what type of fuge you set up, your reef tank is sure to benefit from less nuisance algae, lower nitrate and phosphate and lots of live foods for your fish and corals.