- Water is drained from the display tank through a filter sock to remove food, detritus, organic waste, dust and other particulates.
- Water turbulence is reduced by baffles that also separate chambers and act as a bubble trap. Baffles also keep a constant water level which helps protein skimmers operate efficiently and effectively.
- A refugium light runs opposite of the display tank's daylight schedule to maintain stable pH.
- Macro algae like chaetomorpha or even mangrove trees can be planted in a refugium chamber to absorb nitrate and phosphate from water as they grow.
- Live rock rubble is a breeding ground for microfauna like copepods and amphipods which are a food source for fish, coral and invertebrate. Starfish, sponges and feather dusters may also grow and can help keep water clean by consuming waste particles.
- A substrate containing live marine bacteria is used as a bed to grow macro algae. The substrate acts as a biological filter and, over time, releases trace elements into the system to be used by coral.
- Water is pumped into a protein skimmer to remove organic waste before it breaks down into nitrate and phosphate.
- Water temperature is regulated by a heater. Unsightly equipment, like heaters and protein skimmers, can be set up inside a sump to reduce in-tank clutter for a more natural environment.
- Filtered water is pumped back into the display tank to replenish the aquarium ecosystem with food, clean water and trace elements.
What is a Sump?
One of the most frequently asked questions in the reef aquarium hobby is "What is a sump?"
Much of this confusion stems from the synonymous use of the words sump, wet/dry filter and refugium. Technically all three are sumps by definition, which simply means a reservoir or container of water. The differentiating factors are the purpose and application of the filter.
The aforementioned filters differ dramatically from classic hang-on power filters and canister filters. They are typically located below the display aquarium and are gravity fed with water from a drain in the display tank. When an aquarium is advertised as "reef ready," this typically means it is pre-drilled with an internal overflow box and standpipe installed to drain water from the aquarium into a sump, wet/dry or refugium filter. You can easily add an external overflow boxto your tank if it is not already drilled and reef ready.
A sump is basically a container of water below your aquarium used to house filtration equipment. A sump provides the space to add a larger volume of water to your system, which helps dilute waste and makes it easier to maintain proper water parameters. A sump is also an area where you can incorporate more advanced filtration equipment and techniques beyond what can fit inside or hang-on your aquarium. Another benefit of having a sump is that it allows you to remove a lot of the clutter from inside your aquarium: cords, pumps, probes and heaters can be concealed neatly inside a sump so your display tank has a spacious, natural appearance.
"Berlin" style sumps are the most common type and are highly recommended for reef aquariums. These sumps contain amicron filter sock designed to catch debris (mechanical filtration). Filter socks should be changed out weekly or whenever they become clogged.
The inside of a sump can be divided into different chambers using plastic or glass baffles. These baffles are often removable and can be used to create sections or increase the water volume and depth of the sump. Sections within a sump may be used to house equipment, like a protein skimmer, or to create an area for a refugium. The configuration of chambers/sections varies from user to user, depending on the individual aquarist’s needs. Bioballs and other wet/dry filter media are not found in Berlin style sumps.
The Wet/Dry Filter
Wet/dry systems typically consist of a large reservoir divided into two or more sections. The first section is the biological wet/dry filter area which is a key feature in these types of filters. Additional chambers are used to house equipment like heaters, pumps or protein skimmers.
The way a wet/dry filter works is that water drips directly from the aquarium over a large surface area (bioballs) to promote aerobic bacteria growth. The aerobic bacteria cultivated then processes waste within the system to create nitrates that can be easily removed during water changes.
This is a very effective form of biological filtration method that should only be used with freshwater or fish-only saltwater aquariums. This system can become problematic if large amounts of debris or particulate matter get trapped in the bio media chamber, creating what we in the hobby call "a nitrate factory." Because elevated nitrate levels are hazardous to coral and invertebrate, we do not recommend wet/dry filters for reef aquarium systems.
A refugium is the most dynamic of the filters mentioned in this article because it can be used in conjunction with either a sump or a wet/dry filter system.
Within the reef aquarium hobby, a refugium refers to a chamber inside your sump (or in a separate container) where macroalgae, rubble rock and fine sand or mud is housed to provide biological filtration. In addition to the filtration benefits, refugiums are enormously beneficial to reef tanks because they provide a safe haven for microorganisms, like copepods, to grow and reproduce so they can feed livestock inside your display tank.
Refugiums can be baffled into a sump which is nice because you get the benefits of a refugium and a sump in one.Precision Marine Refugiums/Sumps are a perfect example. They feature three chambers: one for the skimmer, one for the refugium and one for the return pump.
Most refugiums are lined with a fine sand or mud substrate. Small, leftover or broken pieces of live rock, usually referred to in the hobby as "rubble rock," are then added followed by a macroalgae like chaetomorpha (also known as Spaghetti Algae or simply "Chaeto").
You need to provide daylight in the 6,700K–10,000K range for your macroalgae to grow. The photoperiod in your refugium should be opposite of your display tank because it will help prevent pH swings in your system. As time passes, your macroalgae will grow and consume nitrates in the system. Then just prune the algae as needed thereby removing nitrates from your water.
How to Set Up a Refugium, Sump or Wet/Dry System
Now that know what a refugium, sump and wet/dry filter are, you may be anxious to start planning one for your own aquarium system. Good for you! We have a couple of thorough articles on the subject, each with plenty of photographs and hyperlinks to help you with your build. Remember, if you have any questions about refugiums, sumps or wet/dry filters, we are here to help. Feel free to contact us anytime you have a question. We would love to hear from you!