Building a Refugium or Sump
One of the things that plagues most aquariums is the dreaded nitrates. There is no easy way to reduce these chemicals without a large amount of plants or water changes, but most people don't like having plants in the display tank. Or, in some cases, the livestock in the display tank will savagely attack the plants until none remain.
What can be done? One of the answers is to add a refugium or sump. What is a refugium? It is essentially a second smaller aquarium that is placed inside of the stand. This allows several benefits. For one thing, you can add things to the refugium that you couldn't add to the display tank, such as a very deep sand bad, extra live rock, plants, and even small invertebrates such as copepods.
The refugium is connected to the display tank via two pipes. Water can be sent into the refugium via two methods. The first (and arguably the best) is to drill the tank and insert a pipe into the side of the display tank that acts as a drain. The other method is to add an overflow to the display tank, which acts as a siphon. If you use the overflow box method, you should ensure that you get a type that will continue syphoning even after power is lost and resumed.
To return water from the refugium, you need a water pump that has a higher output than the siphon. For example, if the overflow or drain siphons at a rate of 700 gph, you need a pump that can handle, say, 800 gph. You will then have to match the flow to strike a balance between the two pipelines. This can be accomplished by placing a valve after the water pump and closing the pipe until the water level in the refugium remains constant.
But what happens if power is lost and water reverses its way through the pipeline and back into the refugium, causing a flood? This scenario can be preventing by placing a check valve after the water pump, which will only allow water to flow towards the display tank. You could also mount the spout going to the display tank above the waterline, but this would be much more noisy.
Now that the plumbing issues are solved and you have a failsafe design, you have to decide what to put in the refugium. One thing that is recommended is a deep sand bed of 6 inches or more. This depth will allow a large amount of bacteria to accumulate that will remove nitrates from the water. You can also add live rock rubble to the refugium to help filter ammonia and nitrites. A more beneficial use of the refugium, however, would be to add aquatic plants, such as chaeto, a macroalgae. The plants will effectively filter nitrates and keep you water quality very high. An added benefit of the plants is that you can feed them to your fish if they become too numerous.
The refugium can also serve as a breeding ground for tiny food such as copepods. These tiny creatures are food for mandarin dragonets and blennies, but can easily become extinct in the display tank. In the refugium, they can reproduce without the threat of fish and spread to the display tank via the return pipe.
The refugium can also serve as a holding tank for aggressive fish or invertebrates that you don't want in the main tank. For example, if you have a yellow tang that is attacking a new addition to the display tank, you can move the tang to the refugium until the new addition gets used to the tank. Or, if you have a crab that starts attacking your fish, you could put it in the refugium where there is nothing to attack.
Another benefit of refugiums and sumps is the ability to hide your bulky and unsightly equipment. You can put everything from heaters to protein skimmers in the refugium, reducing the amount of space occupied by equipment in your display tank. You can also use larger equipment, such as giant protein skimmers, by placing them in line with the refugium.
In conclusion, it is clear that refugiums offer a wide range of benefits. For a small amount of money, you can create a permanent filter that needs little or no maintenence and will greatly reduce the amount of nitrates in your aquarium.
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