General, Other

Why do people use refugiums in their aquarium? Different types of refugiums and more.

A refugium is a mystery to most budding hobbyists. Most novice hobbyists don’t realize they exist. However, a refugium is a good addition to the aquarium, which you should definitely know more about. In this article, we’ll discuss why people use refugiums, discuss the different types of refugiums people use, and provide general tips and guidelines for using a refugium.

What is a refuge?

Technically, a refugium is a ‘refuge’. A refugium is generally used to provide security for vulnerable species and to protect them from the larger fish in the main aquarium. Refugiums are often used to raise copepods (copepods) as food for fish and coral, or to raise fish or coral. A refugium also serves to filter the water from the main aquarium, to house all of the aquarium’s equipment, or as a way to make water changes easier and safer for the aquarium.

Why should we use a refugium?

There are many instances where having a refugium connected to your main aquarium can be beneficial. Some of these reasons could be:

With additional lighting, algae can be grown and harvested. Growing algae in a refugium helps absorb waste that would otherwise contaminate the main aquarium. You can also ensure that fluctuations in pH are prevented and that the oxygen level in your aquarium is also maintained at night by leaving the light in the refugium on at night. As a result, the algae and seaweeds will produce oxygen and absorb CO2, keeping the pH stable.

Protect small animal organisms from being eaten by fish and coral to develop a stable population in your aquarium. If you don’t have a refugium there is a chance that the entire population will be eaten and your population of small organisms will disappear. Popular organisms that can develop into a stable population in your refugium are amphipods and copepods. In an aquarium, a large enough refugium can provide a safe haven for copepods (where they don’t have to worry about being eaten and can reproduce so that you create a stable population). The copepods can enter the main aquarium, providing a regular and healthy source of food for the animals in your tank.

A refugium increases the total water volume of the aquarium, making the water more stable. For example, a 60 liter aquarium with a 20 liter refugium is actually an 80 liter system; the extra volume makes the aquarium water less sensitive to temperature fluctuations and other disturbances, making it easier to care for an aquarium. The more sensitive fish and corals will certainly benefit from this.

A refugium can serve as a refuge for fish that are vulnerable or prone to bullying (e.g. seahorses). Some owners even place new fish in a refugium to help them acclimate to a quiet environment (away from the inhabitants of the main aquarium). Helps young fish develop in a safe environment as they grow, while at the same time keeping them accustomed to the water and conditions of the main aquarium.

The main types of refugiums

When it comes to setting up a refugium for your tank, there are a few different options to choose from. Refugiums can be divided into the following three types: sump-based, in-tank, and aquarium-suspended refugium. Each type is designed for a specific purpose and is suitable for different types of aquariums. Before choosing a refugium for your tank, take the time to learn the basics of each option below:

sum based

With a sump-based refugium, the refugium is a second aquarium that you place below your main aquarium. This option is recommended when available.

You can place your protein skimmer in your sump.
Keep the pH and oxygen levels in your aquarium stable by leaving the lamp in the refugium on overnight.
You don’t have to worry about how it looks.
Costs the least of the different types of refugiums available (you are basically dealing with a regular aquarium here, not a specialized piece of equipment).

The refugium is often placed out of sight, making control more difficult.
Costs the most if you opt for a high-tech refugium.
Takes up the most space.

The cost depends on how you approach the refugium. If you take a low-tech approach and use a regular aquarium, your price will depend on your materials and size. However, if you go for a high-tech refugium that includes a lift pump and a protein skimmer, this can result in costs of between 300 and 600 euros.


The In-Tank Refugium is the simplest solution for creating a refugium. You basically place a small container in your aquarium for the water to flow through.

Doesn’t take up more space than what you already have.
You can see the little critters and the algae/weeds.
The cheapest option in terms of refugiums.

Does not add water volume to your tank.
Looks unnatural and often not nice in your aquarium.
You cannot run separate lighting schedules for the main aquarium and the refugium.
The price range is about 30 to 50 euros, depending on how big the refugium you buy.


Hang-On Refugiums are loose containers that hang from the back (usually) of the regular tank. They use a pump to move water in and out of the refugium.

With a Hang-On refugium you still share the water between your aquarium and your refugium.
Many aquariums do not have space under the aquarium, this may be your only available out-of-tank refugium option.

Cannot be too big or heavy when hanging from your tank.
May not work with the way you set up your tank relative to the wall (you will need some space behind your tank).
It can also be difficult to clean up spilled water behind the aquarium.
It is a more expensive option than an In-Tank option.
The price range is from 75 to 150 euros, depending on the size of the Hang-On refugium.

Refuge tips and guidelines

Here are some general tips and guidelines for integrating a refugium into your aquarium setup.
Sufficient water must flow through the refugium. The actual flow rate (how many times the water flows through the aquarium) will depend on what you have in your refugium. A basic rule of thumb is to change the refugium water volume in one hour (ie for a 20 liter refugium the water flow rate should be 20 liters per hour).
You can place your skimmer in your refugium. This gives a nicer look to the main aquarium, because you have less equipment in the main aquarium.
In general, with refugiums, bigger is almost always better. Even if you think you don’t need it now. Some experts suggest that the refugium should be 20% of the size of the main tank.

Residents for a Refugium

As you may already know, a refugium can be used for various purposes in the aquarium. One of the most common uses is growing sensitive species or food sources for fish in your aquarium. Some people like to use a refugium to grow certain types of algae to serve as food for marine fish. Refugiums are also used to raise small organisms such as brine shrimp, mysis shrimp, copepods and isopods. A refugium preferably contains different types of algae/weeds and certain scavengers such as shrimp and snails to prevent the accumulation of waste. For small inhabitants such as brine shrimp and copepods, it is useful to separate them so that they are not eaten and you can build a stable population for your aquarium.


Now that you know the basics of a refugium for your aquarium, you may be ready to decide if a refugium is right for your aquarium. A refugium can be used in almost any type of aquarium, be it salt water, fresh water or brackish water. It all depends on what you want to use it for. As you already know, refugiums can be used to house sensitive aquarium inhabitants or to breed certain species separately from the main aquarium. You can also use the refugium as an additional source of filtration for your tank. If you decide that a refugium would also be useful for your tank, take some time to consider what type of refugium is best suited for your aquarium.


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