Salty Q&A: Is a Sump the Same as a Refugium?

QuestionWhat exactly is the difference between a “sump” and a “refugium” (assuming there is a difference)? These are terms I didn’t hear in my 30-plus years as a freshwater aquarist, but I’ve heard them numerous times since starting my first saltwater tank.” – Submitted by Moira B Answer There is a distinction between a sump and refugium in marine aquarium hobby parlance, but sometimes there’s a degree of crossover between these two systems that can make it difficult to tell where one ends and the other begins. Let’s try to define each, and then briefly examine why they sometimes defy easy categorization. Sump defined A sump is a separate (but plumbed into the system) tank or reservoir, situated below the level of the aquarium, that is typically used to hold various life-support equipment—protein skimmer, heater, etc.—so it doesn’t detract from the aesthetics of the display. A sump also provides the added benefit of increasing the water volume of the overall system. Refugium defined A refugium is also a separate tank or reservoir that is plumbed into the aquarium system, but it serves a very different purpose. Essentially, a refugium offers a safe place—a refuge, if you will—in which to sequester organisms for one reason or another. For example, hobbyists might want to create such an environment in order to culture microfauna (such as amphipods and copepods), bolster the system’s biofiltration capacity with additional live rock/sand, grow macroalgae for the purpose of nitrate reduction or feeding herbivorous fish, isolate injured or bullied specimens, or house interesting hitchhikers that may not be welcome in the display tank.

Marine Aquarium Terminology: Activated Carbon vs. Carbon Dosing

Activated carbon and carbon dosing – similar sounding, but different techniques for improving water qualityAs if our hobby weren’t perplexing enough to the average beginner given all the oddball jargon we toss around, things can get doubly befuddling for novices when they come across two or more similar-sounding terms that actually apply to very different concepts. Such confusion could easily arise, for example, when newcomers are first confronted with the concepts of carbon use for chemical filtration and carbon dosing for nitrate/phosphate reduction. So, to help clarify these sound-alike terms, let’s define what they are and how each is used to maximize water quality in a marine aquarium:Chemical filtration with activated carbon Likely, activated carbon is what comes to mind for many new hobbyists when they first hear or read about carbon use in marine aquaria, especially if they have a background in freshwater fishkeeping where activated carbon use is a long-established practice. Activated carbon (aka activated charcoal) is a highly porous medium, typically sold in granular or pelletized form, that is used to remove dissolved organic compounds (DOCs) from aquarium water. It’s considered a chemical filtration medium because the DOC molecules it removes actually form a bond with the surface of the carbon—a process known as adsorption. DOCs are what cause the yellowing of aquarium water, so their removal with activated carbon helps keep the water crystal clear. Activated carbon can also be used to eliminate various toxins and contaminants from the water, for example the noxious chemicals many corals and other sessile organisms release to prevent neighbors from encroaching on their real estate, medications used to treat fish, residual ozone exiting an ozone reactor, etc. There are various ways to place the carbon granules or pellets in a system.
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