So you want to set up a nano reef aquarium? What could be better than a little slice of a tropical ocean on your desk? Loosely defined, a nano reef is a small, less than 30ish gallons, aquarium that contains marine invertebrates and perhaps fish. For this article it will be assumed that the reader has some level of experience with salt water aquaria.
By and far the largest issue of nano reef aquaria is one of scaling. For example, consider the ocean. To the coral polyp, shrimp, or any critter you like, the ocean is essentially infinite in scale. That means that pH, calcium levels and all the other water parameter stay more or less constant and more importantly the water is ideal for the animals you wish to keep. In a so call ‘standard’ reef aquarium with refugium there will be maybe 100 to 200 gallons of water. This is course is vastly smaller than an ocean but is more or less stable when it comes to water chemistry and temperature. Now consider a nano reef aquarium. Folks have setups down to the 2 to 5 gallon range and water chemistry has to be kept to the same basic tolerances as the ocean. The question is how.
Keeping a nano reef aquarium comes down to four basic things; temperature, light, waste loading and water chemistry. Master these and you could conceivably keep acropora in a coffee cup.
Maintaining a nearly constant temperature is critical. A 5 gallon nano reef could very easily over heat in a matter of hours if perhaps its near a sunny window. Alternatively we tend to keep reef aquaria around 80 degrees F. This is a full 10 degrees greater than most folks room temperature. So the aquarium must be heated. How do we heat? There are heaters of course, but do not discount heat generated by pumps and lights. Any ancillary device will add heat. Choose wisely when selecting a heater. It takes about 2.5 watts to heat one gallon of water one degree. As an example let’s say we have a 20 gallon aquarium and we need to make sure, at a minimum, its 10 degrees warmer than the room its in. You would need 500 watts. That does not mean go and buy a 500 watt heater! To raise the temperature in your 20 gallon aquarium from room temperature to operating temperature in one hour, without any other influences you would need a 8.3 watt heater. The point of this is choose the lowest possible wattage heater for your application. Too large a heater and you could have massive temperature fluctuations. It is far better to have a small heater run constantly than have too large a heater.
If you wish to keep photosynthetic organisms you need to provide light that more of less approximates the light that is incident on the ocean. Lights also generate considerable heat. Water tends to absorb light on the red end of the spectrum. What does this mean? Your chosen lighting must be more bluish than sunlight, think atinic bulbs, or 10,000k metal halides. The lighting must not generate considerable heat. In the end there is really only one choice for a nano reef aquarium; LED’s. Metal halides are simply too hot and without a chiller would quickly over heat the water unless hung high above the aquarium. Compact fluorescents are common in nano reefs are certainly workable, but do not discount the heat generated by them as well. In the end LED’s are cool running, very long lasting and available in a wide variety of color temperatures and intensities; and as such are the best choice for a nano reef. You might want to check our guide on the best wifi controlled aquarium lighting.
Put bluntly, all animals poop and all animals die. When you live in an aquarium you are essentially swimming in all that and its not compatible with life. Choose your critters carefully. Waste loading from hard coral is negligible. Soft corals make a little more waste, followed by invertebrates. The really enemy in a nano reef aquarium, when it comes to waste loading, are fish. Those gorgeous, colorful, playful clownfish poop like crazy. As an aquarium keeper it is your job to somehow filter or dilute that waste. But before filtering and dilution its far easier to manage if the waste is not there in the first place. So when stocking your aquarium be aware of this. Choose smaller fish, choose to stock fewer fish. If something dies immediately remove it. Feed sparingly or, once your reef is established don’t feed at all.
Choose fish that are vegetarians and will graze on algae.
Ocean water is full of things that your critters will consume as they live and grow, and your critters will fill the water with things that are toxic to them, as described above. How do we stabilize water chemistry with the small volume within a nano reef aquarium. It comes down to three things; filtration, water changes, and volume.
There are as many filtration schemes as there are fish in the sea. Formerly we used wet dry filter and protein skimmers now the en vogue filtration mechanism is live rock, sand beds and refugiums. Many years ago there were under bottom filters. The good news is they all work, albeit some better than others. Some methods can fail and some are robust, some can remove valuable nutrients as well as undesirable things. What is described following is what I would consider a solid and robust filtration scheme. Use properly cured live rock and sand. This will be the base that your coral will live on. Live rock and sand is well known to clean water via biological processes and introduce numerous small organisms to the aquarium. Just be sure to not add too much as water volume is displaced and your 20 gallon aquarium may only hold 10 gallons after all the live rock and sand in inside. Second I will recommend a small wet dry filter.
This in now considered heresy. But the simple fact is wet dry filters almost instantly convert ammonia into nitrite and nitrate. Now of course nitrates are not good in an aquarium, but its far more acceptable to have nitrate than ammonia. Some will argue that live rock will do the same, in a natural way. This is true. Biological filtration efficiency is largely a function of flow over a surface area, in that regard a wet dry filter is far more efficient than live rock.
Next comes protein skimming. Again recommending a protein skimmer in a nano reef is heresy. But again, simply put, they work. How can you keep a school of 30 clownfish in a 55 gallon aquarium? Skimming! Other than constant water changes, there is no other way. Sure skimming will take out some usable nutrients, but those can be readily added back. Skimming is especially useful if you choose to have a high waste loading due to fish.
Finally we will talk about water volume. Volume is the one parameter you can control that will fix everything. We choose to restrict volume when keeping a nano reef aquarium, but there are several ways around this. First consider adding a refugium. Commonly a refugium is a second aquarium, on an obverse lighting cycle, that contains macro algae and sand beds. Algae and sand help with filtration and water chemistry of course. This is best practice. Even if a refugium with lighting is not practical, please
consider using some mechanism to increase water volume. Even an unlit tank just simply there to increase water volume will be a tremendous boon to the nano reef.
We can also increase the effective water volume with water changes. Much like increasing water volume, water changes can fix almost anything. When setting up for a water change, be sure your water is at the same temperature, has had the chorine removed and been properly aerated. It is wise to consider adding a small piece or live rock or sand to your water change vessel to begin biological processes. The exact volume percentage of water that should be changed and how frequently is largely dependent on waste loading, organisms kept and the aquarists time constraints. For a densely stocked nano reef water changes of 15-25 percent twice a week would be in order.
When doing water changes do not simply drain the tank and dump in new water. This will surely cause issues. When designing a nano reef aquarium, be conscious of the fact the water changes are a necessity . If you have a refugium, design it such that there the normal operation level will allow you to add your desired water change volume directly to the refugium. Once the water has circulated for a few hours the refugium can be drained back to its nominal level.
In the end a nano reef aquarium is a proven concept. Due diligence and some research will help you avoid many of the common pitfalls. Please note that the above is one person’s ideas. There are many other thoughts and techniques that work equally as well. It is your job as an aquarist to find what work for you.