Aquarium In-Sump Refugium Facts & Benefits

Aquarium In-Sump Refugium Facts & Benefits


A typical in-sump refugium in a reef aquarium is a chamber within your sump containing a macroalgae with the primary purpose being to help with biological filtration.

Typical Elements of an In-Sump Refugium

  • Macroalgae such as:
    • Chaetomorpha (Highly recommended)
    • Red Gracilaria
    • Caulerpa
    • Spider Algae
    • Mangrove (not a macroalgae but serves a similar purpose)
  • Micro-organisms such as:
    • Rotifers
    • Copopods
    • Tiger Pods
    • Tisbe Pods
  • Mud or Sand
  • Live Rock
  • Horticulture Light

The Symbiotic Relationship Between a Refugium and Your Display Tank

One of the more troubling nuisances of reef keeping is unwanted algae in your display tank. The biological process of the reef inhabitants ultimately produces wastes that breakdown into phosphate that algae thrive upon. This combined with the excellent light source required to sustain your corals and you have an ideal environment for algae to thrive.

A refugium combats algae by creating an environment outside the display tank to house a more aggressive yet more manageable algae. Additionally, by including micro-organisms such as rotifers, copepods, tiger pods, etc. detritus that makes its way from the display will also be broken down.

Not only does a refugium help absorb harmful waste from your display, but the micro-organisms will make their way back into your display tank and serve as a nutritious source of live food for your fish, corals, and other inhabitants.

How To Set Up a Refugium

Now that you know what makes up a refugium, we need to consider the setup parameters.


Reefers have had success with various kinds of lights, even simple fluorescent bulbs. The best approach however is to purchase as powerful a light as you can afford, within reason of course. A horticulture light is a good choice as it’s light spectrum is designed to best promote the growth of your macroalgae.

Light Cycle

The ideal light cycle should be the inverse of your display tank. As your display lighting begins ramping down your refugium light should begin ramping up. The reason for this is it will help to prevent ph drops when your display tank lighting is off.

Water Flow

Flow through your refugium shouldn’t be brisk. You want to have more prolonged water contact with the macroalgae and not overly disturb the micro-organisms so they can propagate well. A good flow rate would be a turnover of the refugium volume once per hour but I wouldn’t be too concerned about adhering to that very closely. If you have particularly high turnover requirements for your display you may need to divert some of your return flow to bypass the refugium chamber.

Refugium Size

It’s a little difficult to suggest a specific ratio of refugium size to display size although in general having a very small one vs. not having one at all is definitely true. I suppose it’s theoretically possible to have one too large as well but erring on the side of larger is likely the best route to go. Your tank goals may also dictate this some. If you plan to keep voracious pod eaters such as a Mandarin Dragonet you may want to bump up your size a little.

Macroalgae Selection

There are various types to choose from however the most popular choice is Chaetomorpha. Chaeto is popular for a reason. It is very aggressive at consuming phosphate. It maintains itself in a tight mass which makes maintenance much easier and prevents proliferation into the main display tank. Also, unlike some of the other options, it does not go sexual which in short means that it can under certain conditions release harmful nutrients back into your aquarium.

Live Rock & Sand or Mud

These are optional to include depending on your goals but can help with providing a more diverse environment for micro-organisms and bacteria that can aid in the process of breaking down detritus.

Refugium care and maintenance

While ultimately reducing overall maintenance and improving the health of your display aquarium is the main point of a good in-sump refugium, they do still require some attention.


As your macroalgae grows, eventually you will need to remove some. Remember, it’s purpose is to absorb nutrients that would otherwise go into feeding nuisance algae in your display tank. Don’t remove too much as it is also the home for your micro-organisms. Also, you don’t want to dramatically reduce the phosphate absorption ability.


In most situations your micro-organisms will take care of themselves however if you’re caring for a Mandarin Dragonet you may want to feed them phytoplankton. This will help the pods grow more plentiful and increase their nutritional value. You may also find you need to restock the pods if you have a crash or they become eaten more quickly than expected.

In Conclusion

A refugium can be more recommended. Not only will it make your regular maintenance easier but it will make your aquarium healthier and inhabitants happier. Hopefully we’ve answered enough of your questions to get you up and running.

ound of cure. Especially when it comes to any type of reef pest. If you truly want to be rid of all of your bristle worms or fireworms you’ll probably have to go with the nuclear option and start from scratch. That said, traps and predators can be very helpful in getting a large infestation down to a manageable amount. The majority of bristle worms aren’t a problem even if they are unsightly. Learning to live with them is really the best solution.

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