This is the last of the blogs for the recent Care Guide update.
A refugium sump doubles as your filtration system sump that contains your equipment and a refugium. There are about 100 ways to build one and I’ll just give some general guidelines for you to follow and a couple of different examples. Your design is up to you.
What you will need:
A tank of some kind; this can be an aquarium, a strong plastic tote, or a tank you build from scratch. I prefer a tank I can see through.
A light; a daylight spectrum 6500-6700k light is best for this.
Some method of dividing the tank into chambers; this can be sheets of glass or acrylic with the appropriate bonding agents, (silicone or acrylic bonding agent) or it can be smaller tubs or containers that fit into the sump.
Your filter media, this will include the three types of media mentioned at the top of this section, biological mechanical, and chemical.
Your equipment; all of your pumps, skimmers, heaters, etc. necessary to make the system operate.
From the discussion on sumps you already know a pump will sit in your sump or in the plumbing that leads to it. This pump will move water up to the main tank and the main tank will overflow into plumbing that leads to your sump. So you have water flowing out and water flowing in. You want these at opposite ends of your tank. As the water flows through your sump, it will flow through all of the types of media you have in place. It will also flow over your heater and it may get skimmed by your protein skimmer. The path the water takes to get through all this media is up to you.
The refugium in the sump is a large chamber that houses the life you want to protect from your fish. Usually it is set up similar to an aquarium display. This would include a substrate such as sand, live rocks, and possibly mangroves or macroalgae. Remember if your sand is 3 to 6+ inches deep, it forms a low oxygen environment for anaerobic bacteria to live. (Remember an advantage to deep aragonite sand beds is that they dissolve over time releasing calcium into your water.) These bacteria consume nitrate. Often copepods, worms, aiptasia, sponges, and bacteria will populate the refugium without any help from you. You can also buy these items, either in bags or on life rocks. Aiptasia is often a nuisance in your display tank but in your sump, it adds to filtration.
The light goes on top of the refugium chamber. Because the PH of an aquarium falls during dark hours, it is common to set a timer on the light such that the light comes on at night and goes off during the day. Another option is to leave the light on 24 hours a day. This is probably less efficient than having a light cycle but it is simple.
However you design the path for water to flow through your system, always ask yourself, can this chamber get clogged? Where will the water flow if it can’t flow through this chamber? Will it flow onto your floor? To prevent this from becoming a problem, always build a bypass to any clogable chamber. When the chamber clogs, the water level will rise in the prior chamber. By not having that chamber’s walls reach the top of the tank, it will overflow its walls but not the external walls of the tank.
Nutrient Lockup and Export:
The whole point of setting up a refugium is to get nutrients out of the water. The life forms in your refugium do this by consuming the nutrients and making them a part of their biomass. In the process of doing this they lockup the nutrients and prevent them from being available to nuisance organisms such as cyanobacteria that can cover your tank in a matter of hours. A refugium has a limit to the amount of biomass it can house. Once that limit is reached the organisms in your refugium are no longer able to lockup nutrients. You can expand the lockup capacity of your system by feeding biomass from your refugium to your fish. This locks some of the nutrients in the flesh of your fish. It also reduces the amount of nutrients you import into the system by feeding fish foods from outside. Many fish will eat copepods extracted from your refugium with a baster or by your system pumps. Some fish will also eat macroalgae.
Once the lockup capacity of your whole system has been reached, it is time to export nutrients. This is simply a fancy way of saying, take stuff out to make room for growth. Mangrove trees can be trimmed like bonsai trees. Macroalgae can be trimmed and given away or even sold. Live rocks and sponges can be swished in a bucket of seawater to remove excess waste. The substrate can be vacuumed, or sifted a portion at a time. Filter fiber can be replaced. Be careful not to export too much at any one time. This could reduce your system’s lockup rate and cause fluctuations in your water parameters. Also consider that when you clean your display tank, you are also exporting bacteria. This combines the effect of any nutrient export you are doing in your refugium.
Sometimes macroalgae can become toxic if it gets too crowded. Always be mindful of how full your refugium is getting of macroalgae.
The first example of a refugium sump is a 20 gal sump I have running on a 30 gallon tank. This refugium could run a tank much larger than it is running but it is doing a good job. It is made from a 20-gallon aquarium that is divided with glass panels into three chambers. The first chamber is the refugium. Often the first chamber is a mechanical filter. This sump is fed by an overflow box that has sponges in it. That acts as my mechanical pre-filter. Next to the refugium is a media chamber. Here I have an additional sponge, fiber filter, and a bag of carbon. Notice that if the 2nd chamber overflows, it overflows into the 3rd chamber. The third chamber is the pump chamber. The pumps are protected from sucking up gravel by having a chamber all to themselves. There is a heater in the refugium chamber as well as a protein skimmer.
In this design, the water level in the entire system is relatively constant until the water level falls to the height of the wall separating the 1st and 2nd chambers. Then the water level in the 1st chamber remains constant while the last two fall till the pumps suck air. Because the capacity of the last two chambers is much less than the system as a whole, if I see the water level is lower in the last two chambers than the 1st chamber, I know I need to add water immediately. By keeping the heater in the refugium chamber, I know it can never go dry.
The walls forming the chambers are not perfectly vertical. They are put on an angle so that the 2nd chamber is narrower at the top than at the bottom. This is so the sponge can’t float up.
The second example is a 37 gallon aquarium that I didn’t want to permanently divide. It’s a nice tank that I may want to use as a display one day. The tank has two chambers. One houses all of the mechanical and chemical filtration media and the other is the refugium. The heater and pumps both sit in the refugium chamber. The pumps have shields around them to protect them from sucking up substrate and I have the substrate—crushed coral—pushed away from the pumps so they will sit lower.
The first chamber is made from a dollar store garbage can I have hanging on the side of the tank. The overflow from the two display tanks above it falls into this can, through the media inside, and out the holes I drilled in the bottom and bottom of one side. There is pond filter media that is a hard plastic woven wire thing called Matala®. There are 3 densities of this material. A bag of carbon sits on top of the Matala® and a fiber pad sits on top of the bag. The fiber pad clogs up with waste and I rinse it in the sink. The garbage can sits lower than the sides of the tank, so if it overflows, it overflows into the refugium chamber.
There isn’t much to explain about the refugium chamber. It contains the crushed coral mentioned above, some rocks, and a few red mangroves. The heater is down low in front, the pumps are off to one side. The protein skimmer is not in the sump. One of the pumps in the refugium leads to the protein skimmer and it dumps into the lower tank. This allows the pump to perform two tasks at once. It runs the protein skimmer and it provides circulation for the system. As the water exits the protein skimmer, it flows through a second garbage can with Matala® and fiber but not carbon.