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Variations on a Refugium: Installation Options

Extra Extra!Variations on a Refugium: Installation Options
By: Steven Pro

I am an equipment junky. Don’t get that confused with a technology buff, though. I hate gadgets. I don’t use electronic probes to monitor my display’s pH, ORP, temperature, salinity, or anything else. A refractometer and simple colorimetric test kits work good enough for me. I don’t even use a mechanized top-off unit. Starting a slow siphon each morning before the lights come on to dose kalkwasser and keep up with evaporation works just fine and I don’t see a reason to change. The fewer gizmos you use, the fewer things can malfunction or break. I am an advocate of the keep it simple mentality. But, I do appreciate something that is well designed and constructed, that performs superbly and efficiently, and is also a good value for the price. In that sense, I love to check out the latest pieces of technology, see how they work, and evaluate if I need one. So, while I leave my good friend Anthony Calfo to discuss the pro’s and con’s of the livestock common in refugia, I am going to focus on the more mechanical aspects of refugium technology.

In this first installment, I am going to discuss the various locations one could place a refugium in relation to the main display and the inherent positives and negatives about each installation option. There are basically three places to put a refugium; above the tank, below the tank, or beside the tank. Any of these can be a desirable addition to the overall aquatic system. It is just that some of these locations are better for certain desired applications, while others excel in different ones. Let us take a look at these refugium installation options.

Below Tank

If the aquarium already has a sump setup, a below tank refugium is the easiest to install as well as the easiest to hide. It is this second quality which lends itself to this type of refugium being a true working refugium. If it does not have to be attractive, then the only concern is to maximize production and usefulness. Since they are hidden, than can be ugly and not detract from the rest of the display. Plus, it will save you the ear beating you would get from your better half if it was a visible eye sore.

This type of layout is also the most versatile. Any commercially available stand could hold and conceal a below tank refugium. This design could also easily be incorporated in a sump system when the tank is in a wall with a fish room behind it or when the plumbing is all run to the basement. Any aquarium that already has or is planned to have a sump can also have a below tank refugium.

A typical below tank refugium that is sectioned off in the sump for the tank. This is the most commonly used refugium system since most tanks already incorporate sumps and the refugium does not require a seperate vessel. In this combination, the sump is sectioned off with 3 chambers: the first accepts the drain water from the display and contains the protein skimmer, the second is the refugium followed by a series of baffles to help remove any bubbles, and the last section is just for water. This last section is where the water level drops with evaporation. Photo and caption by Gene Schwartz

Below tank refugiums usually receive raw feed water from the display. This water is rich in organics from surface tension at the air water interface as well as heavy in stirred up detritus or excess food that gets swept into the overflow. Hence, this design is great for nutrient uptake and removal. Fast growing macroalgae like Chaetomorpha or Caulerpa can utilize these nutrients and convert them into living tissue for easy removal from the system. You will also notice that in dense growths of algae a variety of critters are attracted to this ever-flowing food source. Mini brittle stars, amphipods, copepods, and mysis shrimp are some of the most common ones you will find in amongst the macroalgae growths. Again, these living creatures are there to grab a hold of any available food and convert that into living tissue. While they are unable to use every portion of that food to create tissue and do create some waste products, they are living amongst the macroalgae. In effect, the algae is capable of consuming some of their waste products just the same as the overflowing waste from the display in a symbiotic-like relationship. Additionally, below tank refugiums with their normal multitude of baffles to trap and eliminate bubbles also tend to trap detritus. In effect, these baffles tend to operate as a settling chamber and when the hobbyist routinely siphons out this debris, they further facilitate nutrient export. As you can see, these below display designs operate optimally for nutrient export. And while they do harbor a number and diversity of planktonic lifeforms, to get up into the display they must pass through the return pump. This surely impacts the number of viable specimens that make their way into the display even though the exact amount of impact is debatable. Sperm, eggs, and small larvae could conceivably pass through unharmed, but larger adults are likely to become shredded. Although pulverized, dead crustaceans are still edible just as live, whole ones are, if the intent is a steady supply of live plankton to feed into the display, there are better placement options, which leads me to discuss the next installation option.

Above Tank

This design is by far the best for introducing live plankton into the display because they are gently gravity fed into the aquarium from the refugium versus traveling through the pump to make their way into the display. This ensures that both offspring, reproductive material (eggs and sperm), and adults alike can re-colonize the heavily grazed and preyed upon display. For as good as this layout is for plankton production, it unfortunately is not nearly as good for nutrient uptake and removal as the below tank design assuming that the system utilizes both a sump and above tank refugium. In this scenario, the water coming to the refugium from the sump is likely to already be heavily scrubbed of nutrients by the sump’s protein skimmer, by chemical filtration media located there, mechanical filtration, and/or possibly another refugium.

The other drawback to this layout is it is not as easily incorporated into most displays. It can be retrofitted fairly painlessly into tanks that are built into a wall. In these instances, a portion of the return pumps water can be diverted and sent to a secondary aquarium mounted on a secure shelf above the display. Unfortunately, not all of us have setups such as this. Most hobbyists are working with commercially available aquarium and stand kits. This makes creating a seamless appearance of an above tank refugium with a display tank difficult.

Best of Both Worlds

It should not be a great leap in logic to see that combining two refugiums, one above tank and one below tank, will theoretically yield the best results. It just takes some planning and forethought to incorporate both and is not easily retrofitted into existing displays unless you have a considerable amount of room to work with, as is the case with in the wall designs. But, two refugiums also gives you additional options as far as differing the substrates in each or varying the lighting schedules (all subjects that will be discussed in future editions). For instance, the below tank refugium could focus on macroalgae growth while the above tank refugium’s primary goal was generating amphipods, copepods, and mysis shrimp. Or, the below tank refugium could grow macroalgae with a 24/7 lighting schedule while the above tank one could operate without lighting to create a cryptic zone that promotes feather dusters and/or sponges for their filter feeding capacity. Truly, the options are limitless. One only needs to research a little to custom tailor a refugium package that best suits their specific aquatic pets’ needs.

There is yet another option when it comes to locating a refugium. One could install it beside the display tank, in effect creating a second smaller display. This is a display in and of itself, so the final appearance is important while plankton generation or nutrient export are secondary concerns. This would be a refugium in the broadest sense of the term. It would simply be a place of refuge for a specimen or species that could not be housed in the main display for whatever reason. One could seek to showcase something unusual, beautiful, or small that would otherwise be lost in the larger display tank. For instance, there are many smaller shrimp that are less bold and would not be as easily observed in a large aquarium but could become a focal point of a smaller display. Harlequin and Sexy shrimp are two that come to mind. Additionally, this smaller display could house a Mantis shrimp that would problematic in the main aquarium, but could be safely housed here. Also, you could design this refugium mostly for the beauty and appreciation of unusual plants and animals, for biotopic displays, or an attempt to build a larger reef ecosystem. For instance, a lagoon for seagrasses, mangroves, urchins, snails, seastars, etc. would be appealing, interesting, and unusual.

These types of refugiums are easy enough to install. Simply get another tank and stand that matches the main display, place them near enough to one another to plumb them to a common sump, and you are done. While you won’t contribute much in the way of plankton generation or nutrient export, you will increase the total gallons of the system, which increases stability. Plus, you have added to the beauty and your personal admiration of your display and there is something to be said for that.
Hang on back refugiums can fall under either the above tank or below tank category depending on their exact configuration. If the water is pumped from the display into the refugium and allowed to gravity flow back into the aquarium, than it is technically an above tank refugium. On the other hand, there are designs which use a siphon to draw water into the refugium and then have a pump return the water back into the display. These would have to be considered below tank refugiums. Regardless of which type the hang on refugium is, these tend to have additional limitations. They are generally small because weight bearing down on the display aquarium is a real concern. As such, their ability to produce plankton and/or grow macroalgae is restricted. But in my opinion, any refugium is better than none.

Hang on the back refugiums have grown in popularity mainly because they are easy to add to an already running marine aquarium. These refugiums are effective, but limited in size. They can be used to hold a small sand bed, some liverock rubble and various macroalgae for nutrient export. Photo by orion25. Caption by Gene Schwartz
On the positive side, these refugiums are extremely easy to install as long as there is sufficient room between the display and any walls behind it. Also, for smaller aquaria, sumpless systems, or undrilled tanks (I will save you all from my rant against siphon overflows), they are the best solution for incorporating a refugium into the overall system.

You should be able to see now that there is a range of options as far as where to locate a refugium. And hopefully, I have sufficiently laid out the pros and cons of each installation option such that you can make an educated decision as to which one best suits your tank’s needs. And lastly, any refugium is better than none, so decide which location can work for you and get to work.

Steven Pro