XV. Refugiums - All Natural Nutrient Control
This article discussed Refugium Concept, Construction & Maintenance
In an attempt to emulate nature as much as possible many aquarists turn to refugiums as a supplementary filter. When employed properly a refugium serves to reduce waste, increase microbial biodiversity as well as serve for a haven for baby fish and settling invertebrates. Construction of a refugium is fairly simple and one can be retrofitted to most systems with relative ease. Refugiums offer additional benefits to your tank with very little extra on the part of the aquarist and it is easy to see why this popular feature is sworn by in some circles.
Concept
With a well-stocked aquarium we have a plethora of mouths, from invertebrates to fish and coral. All these mouths consume food and this food gets turned into waste. In the ocean, a really, really deep sand bed and thousands of pounds of rock serve to allow anaerobic bacteria that thrive on nitrates a safe haven free from disruption. In an aquarium, such means are obviously impossible but the same principles can be scaled down to suit our needs. In a separate aquarium, a deep sand bed, undisturbed by fish and currents can settle and water can be passed through this tank and the bacteria are able to then feed on the available nitrates.
In addition, macroalgae which would be greedily devoured by any herbivorous tank inhabitants can be allowed to grow freely. Macroalgae require both nitrate and phosphate to sustain growth in effect locking these nutrients away in their tissue to be safely exported through harvests. Similarly, the various bacteria of our tank often create microscopic films on the rock work, these films serve as a feeding ground for protozoans as well as flypaper for small particulate organic compounds. This serves as a dinner bell to copepods and helps to sustain a healthy population in the refugium that can be fed to the tank inhabitants.
Construction
To add a refugium there are two approaches, the in-sump refugium, and the flow through refugium. If your sump does not have a built0in refugium, but you have a lot of vacant space, you may consider adding a container to the sump to serve as a refugium. The container needs to be perforated starting a few inches above the sand to allow water to pass through. Looking at in-sump refugiums should give you an idea of the objective and the materials to build a sump from scratch with a built-in refugium may be comparable to setting up a flow through refugium. With a flow-through refugium, water from the primary display is drained into the refugium either completely or with some level of a bypass. Due to the consistent flow of water expected through the system a drilled tank with appropriate drain fittings is best. Additionally, because a deep sand bed is desired, taller tank configurations suit refugiums best.
However, with any option constructing the refugium begins by placing several large rocks on the bottom of the tank and filling around them with sand similar to any tank startup, however, the sand bed should be significantly deeper than four inches if denitrifying effects are desired. Build upon your existing base with a few pieces of quality well-cured live rock and scatter shell litter and rock rubble along the sand bed. Once in its final position either below, alongside or above your tank, plumb the refugium into the sump first and fill the tank with clean treated saltwater until it begins to overflow into the sump. At this point, you may shut off power to the system and plumb a return from your display tank to the refugium. When plumped, power the system back on, you may have to add a small amount of clean treated saltwater to obtain the desired operating water level throughout the system. Lastly, mount a quality light fixture to the refugium setting it to a photoperiod opposite of your tank lighting and place your macroalgae in the tank.
Maintenance
In the coming days you will notice new growth on the algae and on close inspection, you may see smaller critters like copepods and amphipods skittering along the rocks, a hard to spot detail in tanks with fish picking them from the rocks at every opportunity. These "pods" can be harvested and collected by weighing small pieces of Makrolon(a corrugated plastic similar to cardboard in design)to the bottom of the tank. Once a month remove a piece or two and shake them out in the tank. This process is not necessary but many fish will appreciate the treat of live food to hunt and chase. Algae-based maintenance is more involved, but fortunately, not by much.
As macroalgae grow they can form dense thickets of seaweed. Left to grow and macroalgae may grow to suffocate drainage, interfere with powerheads and pumps, or grow to a point that it shades itself and part of the growth dies off. Drainage, pumps and powerhead interference comes with the risk of overflows and equipment failure while dying off of algae will result in a spike of nutrients that were once locked up in the algae. To avoid the above, routine trimming of the algae should be performed. The growth rate of the algae in your refugium will dictate the frequency required however I would consider doing this at least once a month. The algae should not be fed to the tank as it will only serve to reintroduce these nutrients to the aquarium, instead it should be disposed of.
It should be noted here that in many parts of the world certain macroalgae are considered invasive species, as a result, they are heavily regulated and great care should be taken to assure that we do not introduce any algae species to local bodies of water. Never flush algae or introduce it to sewer drains, algae should instead be thrown away or ideally composted after harvesting. For best results consider Chaetomorpha or Gracilaria if available in your area. Both are fast growing to absorb a large number of nutrients but lack the cyclical mass die-offs of various Caulerpa species.
When set-up and maintained properly a refugium offers several benefits to the reef aquarist. With equipment readily available or perhaps even on-hand for some aquarist, this quick project can be carried out effectively during a water change if all components are available and ready to install. The results are lower overall nutrients, a more stable pH and salinity, higher biodiversity and an intake source of pods for feeding. As a final note, more and more hobbyists are incorporating "over-head" sumps into their systems. The primary focus of these systems appears to be more for pod production and introduction to the display tank and less for nutrient control, however, any live rock and sand added to a system will inevitably accomplish this to some extent. Wherever you put a refugium or however you choose to set it up the benefits will be readily visible through the growth of pods and algae in the refugium and the maintenance of lower nutrient levels in your tank.