The Refugium is a mystery to most beginner fish tank owners. Most hobbyists just starting out are so overwhelmed with the basics of fish-keeping, that they don't even realize that they exist.

 In this article, we will discuss why people use refugiums with their aquariums, go over the different types of refugium set-ups that people use, and provide general tips and guidelines with using a refugium with your tank. We'll end the article with a list of our favorite online sources for refugiums.

What is a Refugium?

 Technically speaking, a refugium is a 'refuge" in the sense that while it shares the water of the main tank, it is somehow set off from the tank, to provide the creatures inside refuge from larger fish in the main tank. Because in the more general sense, a refuge is an extra tank or compartment of your tank.

Why use Refugiums?

 You may be wondering -why not just keep a separate tank? The many compelling reasons why a connected refugium is more beneficial:

• With additional lighting, can be used to grow algae to harvest. Growing algae in a sump/refugium also helps absorb waste that would otherwise pollute the main tank.
• Protect small organisms so that they can be self-replenishing. This works especially when you want to grow "feeder" organisms to a certain size so that they can reproduce before the entire population is eaten. Popular "feeder" organisms include feeder fish, amphipods, and copepods. For example: in a reef tank, a large enough refugium can provide a safe haven for copepods (where they do not have to worry about being eaten and can breed). When the refugium is "stirred" (i.e., when you trim the macro-algae in the refugium), copepods will enter the water stream and makes their way back into the main tank, providing a regular source of sustenance for the larger organisms.
• When used as a sump pump, plays a crucial part of water flow for reef tanks.
• Increases overall water volume of aquarium, making it more stable. For example a 60 gallon tank with a 10 gallon refugium is actually a 70 gallon system; the extra volume makes the tank water less susceptible to variances in temperature and other disturbances.
• Separate fish that are delicate or prone to bullying (for example, seahorses) on their own. Some owners even place new fish in a refugium to help them acclimatize in a quieter environment (away from the inhabitants of the main tank). Helps fry develop in a safe habitat as they grow, while keeping them accustomed to the water/conditions of the main tank.

Main Types of Refugiums

 Refugiums can be categorized into the following three types: sump based, in-tank, and hang-on. Let's look at each type in detail.

Sump Based

 With a sump based refugium, the refugium is a second tank which you place below your real tank. This "work" tank is usually kept under wraps and handles your water pump action for reef tanks as well as manages extra filtration.

• Pros - Can keep your skinners in here; run a reverse photosynthesis set-up for your algae; not worry about how it looks; costs the least out of the different types of refugiums available if you go low-tech (you're basically dealing with a regular tank here, not a specialized piece of equipment).
• Cons - You might forget to check your little fry as often as you should if you are keeping them down here; Costs the most if you go with a high-tech refugium sump pump option
• Cost - Depends on how you approach the refugium idea. If you go with a low tech approach and use a plain tank, your price depends on your materials and size. However, if you go high-tech with a refugium that incorporates the sump pump and a protein skimmer, the resulting cost can be in the $350 - $600 range. The extra cost is for a "ready to run" tank with all the parts and plumbing ready to go.

In-Tank

 The In-Tank Refugium is the simplest solution for refugium. You basically place a small container into your tank that lets the water in and out but keeps the critters in and your bigger fish out.

• Pros - Doesn't take up any more space than what you already have; you can enjoy seeing the little fry or other little critters growing in here; cheaper than a hang-on type refugiums
• Cons - Doesn't add water volume to your tank. Looks unnatural. Can't run separate lighting schedules for the main tank and the refugium.
• Cost - Price range is $35 to $50 depending on how big of a refugium you buy.

Hang-On

 Hang-On Tanks work just like their name; they are separate containers that hang-on to the back (typically) of the regular tank. The use an extra pump to move water in and out of the refugium.

• Pros - With the Hang-On refugium, you still share the water between your tank and your refugium. Many tanks and stands aren't fitted with a sump, so this may be your only available out-of-tank refugium option.
• Cons - Can't be too big or heavy if they're going to hang on to your tank; may not work with how you have your tank set-up relative to the wall (you'll need some space behind your tank to fiddle with the refugium). Can also be hard to clean water spills behind the tank. More expensive option than an in-tank option.
• Cost - Price range is $75 to $150 depending on how big of a hang-on refugium you pick up.

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