Refugiums in a Saltwater Tank: Viable Nutrient Control or Just a Safe Harbor?


Refugiums in a saltwater tank are very common, and often misunderstood. From the types of algae to put in them to how to light them, debates about refugiums are always raging.

What’s my take on the topics of the refugium debate? Well, I’ll show you.

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Comments for this article (77)

  • Travis…I’m familiar miracle mud and I’m not a fan of sand in a refugium. Therefore, save your money.

  • Mike says:

    Mark,
    I know you mention making sure your refugium is big enough to make an impact on your tank for Nitrates, Phosphates and PH and I love your plus one concept. I have a 150 gal reef display tank and am building a 80 gal sump/refugium which will be plumbed in the basement. I have about 24″ x 18″ set aside for the refugium. Do you think that will be a nice size for me? Over all length is 48″, so I will have 12″ on either side of Refugium for skimmer, BRS GFO reactors, and my chiller.

  • Mike…what’s the depth of water going to be in your refugium?

  • Mike says:

    Mark,
    Looks like 12″ of water maybe 13

    So the actual refugium will be 24w x 18d x 12h (water level)
    That should give me a 22 gal refugium

  • Mike…that’s a nice size fuge for your tank. I would suspect it can have a good impact on your nitrate levels assuming you don’t trash your tank by overfeeding, overstocking, etc.

  • Mike says:

    Perfect, This is the weekend to get it up and running. Since I am always fighting Nitrates (overfed Anthias and slight overstock) I was thinking of going with DSB. I see you like rock rubble. Thoughts?

  • Mike…go the rubble route. I’m not a fan of DSBs.

  • Jeremy Cowick says:

    How much flow should a refugium/sump have running through it. Is 5x a good rule of thumb?

  • mike patenaude says:

    Hi just was checking out one of your show on refugiums just wondering do you test for iron in your refugium and add as need or not thanks mike

  • I don’t check for iron. If you keep up with regular water changes then your iron levels should be kept in check

  • Chris Flammia says:

    Hi Mark,
    Love your no nonsense approach to this hobby and the way you give us the straight answers with no bs. Before I found your site I was planning on running a refugium in my 20 gal sump for my 75 gal dt. I’m currently running my sump Berlin style. I’m not sure if this sump would be big enough to make any impact on my nitrate & phosphate levels. Reading your guides and watching your videos I see little mention of refugiums and notice that your current build no longer uses one. Do you find they are not worth running? The idea of growing copepods to feed the fish seems interesting. Is it worth it?

  • Thanks for the note and kind words Chris. For a 74g tank, a 20g refugium would be a good size. I would expect it to make a noticeable impact on your nutrient levels.

    And…i’ve got enough rock in my tank that I can keep enough pods around for the fish that need them.

  • Chris Flammia says:

    The total volume of my sump is 20g. The refugium section in the middle is aprox 15″x8″ and runs around 11″ deep. By my calculations that is around 6g for the refugium. That probably would not be enough?

    I have 100lbs of live rock in my 75g tank. Is that enough to keep enough pods for something like a Mandarin?

  • Chris…a fuge of that size won’t do all that much for nutrient levels. I can provide a home for pods to live and populate.

    As far as keeping a mandarin, I suggest only purchasing a mandarin that will eat frozen food. More specifically, if you buy it locally, ask the fish store clerk to feed the fish and see if it eats the frozen food. If it won’t eat the frozen food, don’t buy it.

  • Tennfan1125 says:

    Hello, Im looking to set up my first refugium tank. I have a 55 gal main tank. what size should my refugium be. who or where do you recommend buying the tank from?

    thanks again,
    Dave

  • Curt Ireton says:

    Mark,
    I have a 250 gal DT and a 150 gal sump. I have let my tank get away from me over the last year and had a large red algae out break. All of my live rock is covered with red slime. I am in the process of cleaning the rock now. I was thinking about cleaning out the refugium and replacing the mud with live rock. I could also use a little help on how to clean the rocks or can I just put them in the refugium. My hope is that in the refugium the red algae will die of slowly. Any help would be great.
    Thanks

  • Michael West says:

    Hello Mark …I do truly respect you for your knowledge..And pray for many blessing that will come your way cause you CARE and what to help people..
    That’s said I’m new to this! Always wanted a Big Tank!! Got a 185 gal and 40 gal that I what to use as a refugium. As far as the pumps…(1) rio 2500…(1) Danner 12.B…(1) Eheim I think it’s one of the 1200 series( It’s outside/COLD. I could get back to you on that )
    Skimmer.. AquaC EV-1000 ..recommended to be run outside the tank…(it’s as big as a fire hydrant)
    Media…(2) gal refugium mineral mud…..(20) pounds caribSea arag-alive ..(5) gal of crushed sand and coral mixed
    (1) 36 watt uv sterilizer…(1) vortech mp40w…(2) vortech mp20
    I could use your advise on setting this up. My refugiun will be section off to prevent the mud and sand to flow from it! I know you don’t use mud /sand I got this stuff before I found out about YOU! The main tank has (2) returns..After reading about the sump maybe I should use a 55 gal instead of a 40 gal ..any way your help will be a blessing ..I know this is a lot maybe I should of broke it up a little. but thanks again

  • Barbara says:

    Hi Mark,
    I emailed you but was not sure you responded to emails that you send your newsletters out on. I am new to this hobby..about 5 months. I have a 42 gal hex. I have 4 fish with live rock and some soft corals and 2 anemones. I was concerned about my Nitrates so I just replaced my biowheel filter with an overflow box going to a sump with a little live sand and live rock crumbles and a few plants. My LFS said I do not need a protein skimmer. Is this enough to keep my tank free of nitrates and all happy? It is kind of noisy being in my living room 🙁

  • Dan says:

    Hi Mark,

    I just finished your excellent book on algae control. I have a 60g and a 180g both share the same filtration system. I have small amounts of cyano in my 75 gallon refugium(1/3 of my water runs through the refugium, and 2/3 run through my protein skimmer and rubble and mechanical filtration. the water is then mixed and pumped back into both tanks. There are no signs of cyano in my display tanks. The amount of cyano in the refugium is pretty minor, I have been using a turkey baster to control it every few days when I see an area of carpet.

    I used red slime remover about a year ago, it worked very well. I had a RODI unit fail and my auto top off water got contaminated. All of my tanks had an outbreak at that time. I think the trigger this time was 2 hermit crabs in my refugium died and shortly after I noticed the outbreak. I think this is why the outbreak started there (I have 2 tangs, 2 rabbits, 1 angel, 6 clowns and 2 blennies total, between the 2 tanks(240g) I don’t think it is over stocking issue). My tests are all good but after reading the book I’m not so sure.

    I want to try 3 days of darkness in my refugium. Do you think that would work? I also have a 20-25 lbs of chaetomorpha and Caulerpa in it. Can I leave my macro algae in while I do the darkness? If I take it out and put it back after 3 days I’m pretty sure there will be cyano hidden within it and the cycle would start over? I have heard when you have Caulerpa you should always keep the refugium light on 24/7. BTW is that true? Can I turn my Refugium lights off at night with the rest of my lights?

    Sorry for the length
    Dan

  • Barbara says:

    Dan, I have Caulerpa taxifolia in my refugium and I turn my lights on at night when the display tank light is off and turn it off during the day. This is suppose to help keep the PH levels stable. I have never had any issues with the Caulerpa having the lights off during the day.

  • Dan…I used to run caulerpa in my fuge and you can turn the lights off on it and it will be ok. As far as 3 DD in the fuge, if the cyano is minor, I wouldn’t worry about trying to starve it out. Cyano is everywhere so even if you remove the algae, don’t be surprised if it comes back.

  • Dan says:

    Thanks Mark and Barbara,

    I’ve updated my apex and am going to run my refugium lights opposite my tank lights. I’ll keep an eye on the cyano for the time being.

  • Lyle says:

    I did the same thing as far as letting one of my tanks get away from me! Setup a new tank and the other tank got treated like the red headed step child! LOL! In the process now of getting my RO/DI system setup and correcting the abuse issue! On the abused tank there is a wet/dry with rock no balls, A 20 gallon long refugium and a large hang on refugium that I was cycling off of the 20 gallon one! I suspect that the only reason the tank didn’t crash was from the way over kill filtration system! I can harvest caulerpa every 3 -4 days to feed my fish! Amazing! Glad I didn’t lose the tank! Back on track now!

  • Dan says:

    Just an update if anyone is interested, turning the lights off opposite my main lights not only controls my temp better, my fan rarely comes on anymore, it also seems to have taken the last food source from my cyano. It has died off with no other changes to the tank. I can’t find any traces in the refugium. Thanks for the tip… OBTW my caulerpa is growing just a fast as before.

  • Barbara says:

    awesome! Thanks for the update!

  • Savario says:

    Hi Mark,

    I have a question about your video here… You mention low flow into and out of the refuge but how is this achieved? I am new to the hobby, so new in fact I am just starting the research into it. I have a 20g tank that was previously freshwater. If I can find a 15g tank that will fit under my stand I intend to go with that, if not a 10g, I will DIY the baffles and such. Do you think 10g will be sufficient, if I make the refuge area the largest part of water volume? Love your videos btw str8 forward and no BS I think I’m gonna like it here 😉

    Thanks for the help

  • George says:

    I am starting my 50 gallon FOWLR tank and getting rid of my wet/dry filter and going to a refugium sump and protein skimmer. Will a 15 gallon refugium be large enough to my tank?

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