Sump Or Refugium?


All aquarists know the difference between a reef, mixed reef and fish only aquarium. However, confusion arises on occasion about the sump and refugium.

There are many systems of whatever type that include a sump. Usually they are put there in the design stage and this is really the easiest option, as feeding seawater to and from the sump is more easily arranged.

The sump is defined by the Oxford dictionary as ‘…a pit for collecting water etc’. That’s fairly accurate I suppose in relation to marine systems, one of the attributes of a sump is that it increases the net seawater gallonage of the system which is good for quality. In addition to this it permits items of hardware such as protein skimmers and heaters to be placed out of sight, which is good for the main display.

This is where the confusion starts. In addition to equipment, a sump could also be used for a deep sand bed (DSB) and could also grow macro algae. Then an addition could be made by using a partition and installing a ‘refugium’. The aquarist declares that he has a refugium.

I don’t want to be over-finicky, but is this correct? It is understandable certainly, as a refugium is a place where small life forms can live away from the predations of fish etc. Over and over it is said that small life forms are essential for the health of the DSB. There aren’t any fish in the sump so the small life forms are protected, so maybe it has become a refugium!

In the dictionary version I have ‘refugium’ is not given but no matter, let’s look at ‘refuge’. The definition of this is ‘…shelter from danger, pursuit or trouble.’ So the refugium is a specific not a general item.

Back to the sump then, as said it is primarily added to the system to increase net seawater gallonage and provide an area where heaters etc can go. If the aquarist wishes to add a DSB then fine and the same goes for macro algae. This makes the sump …a sump. It has been added for specific purposes, not one particular purpose.

A refugium is an additional aquarium or container that has been added to the system in the same way as a sump. However, in this case it is intended primarily as a refugium, nothing else. A fish only aquarium is an environment for fish, a mixed reef an environment for fish and corals. The refugium is an environment designed for small life forms. It keeps them safe from predation by fish and permits them to develop and flourish. At the same time, of course, it also increases the net seawater gallonage of the system.

So if the system is to include a sump and a refugium, there should be three aquariums. The largest one will be the display aquarium of whatever type, and attached to this and fed seawater by it will be a sump and a refugium. The major advantage of the two, apart from increased seawater gallonage, is space. There is more space for equipment in the sump if it is not being used for so many purposes, and there is more space in the refugium for the creation of the special environment.

Overall though, it could be argued that the above is a terrific example of nit picking! Truth of the matter is, the sump doesn’t have strict boundaries and could be and often is used for a DSB and macro algae, with lots of tiny life forms. These life forms are protected from fish predation so it is a refuge. The specific refugium is different because it is only that, a refuge, nothing else. The refugium, as it is for one purpose only, may well offer greater space for the created environment, which in turn permits more life to develop, which could mean a higher amount of live food (that which finds its way into the main display aquarium).

I would love to have a three tank system but haven’t the space. Those who have the space, great! Those aquarists who use a sump only, no problem, let’s not argue about a name.

  1. John,

    I like to think of the Sump as being a volume of water separate from the display tank. Now you may have a sump or a sump and refugium. A typical sump might have bioballs and a protein skimmer, but a Sump and Refugium would also contain the sandbed and macroalgae. A refugium would also be contained within the sump.

  2. Nothing wrong with that! The majority of aquarists I would guess see a sump in just that way. Having a sump and a refugium within it is quite common practice. Nevertheless, it would be great to have a three tank system – or at least it would be ghreat as far as I’m concerned anyway.

    Johns last blog post..The Banggai Cardinal At Risk?

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