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)

  • paul says:

    whats your though on sea hair,to get rid of hair algae

  • Brent says:

    Is there a recommended size ratio for refugiums versus display tank? You mentioned about the HOB one you had in the past being too small…should they be avoided all together?

  • Bill says:

    Great video as always! I’ve reached some of the same conclusions but there sure are a lot of opinions out there. I think it’s important for everyone to do there research and form an informed opinion.

  • Eli says:

    Good info. I recently was looking into outing one on my tank

  • Brent…I’ve never seen a recommended size and I always say the bigger the better. The HOB one I used was a nice pod farm and but I didn’t see a change in tank parameters.

  • They can work well, but it doesn’t get to the heart of the problem.

  • Devin says:

    Hi Mark-
    Great video!! I have a 155 gallon tank with my refugium running Chaeto, a DSB, few pieces of LR and I have a few blue legged crabs in to help with the detritus, but mostly for looks since I heard they don’t do much. My question is what are the pros and cons of running my fuge lights 24/7…which I currently do?


  • Murat says:

    hmm…”couple of inches” refigium 🙂 lol you mean it…

  • Brian says:

    I have to strongly agree with the bigger the better. Not only will you increase your total volume, but nobody has said ‘Shucks, I wish I had less space down here’

    I just added hardware to my already overcrowded sump, it is just too small, but it is the largest one that will fit in my cabinet.

    In this case, don’t just +1.

  • Bob says:

    I just got a 150g tank that is going to become the new sump/fuge for my 225g DT. I am going to build a new stand around it to make sure it fits. Once I do this I will get rid of my tiny 75g sump. Right now I have about 20g worth of fuge in my sump, I want to up that to 60+ gallons, and also have room for much more equipment. As Brian said I have never wished for less room.

  • Bob says:

    BTW, what are your thoughts on an Algae Turf Scrubber?

  • Great subject Mark.
    some weeks ago I made a fairly big fuge for my system.
    Since then my tank has really started to shine.
    saying that I absolutly saw both phosphat and nitrate levels drop near undetectable levels.
    Chaethomorpha, gravity feeding lowflow, no return pump blending pods to death.
    thus giving lots of live food for corals and fish.
    In my case, this has worked very very well.

    Love your tank man.
    keep up them good reef vids.

  • Chris says:

    a great show Refugiums is one of the things i really did not understand to well.with useing Live Rock Rubble in the Refugium do you have to worry about dead spots? can you just put a lot of Chaeto with not rocks,sand or mud and still be good?

  • Daragh says:

    Hi Mark

    I recently lost all my livestock in a hydrogen sulphide incident so I’m now looking at setting up a refugium during the “downtime”. Can I run it with bio pellets and is it pointless having a phos reactor running in conjunction or is that just double jobbing.

  • Jordan says:

    I can agree 100%! When I had my 65gal I had a sump on the side of the tank and an external refugium under the tank and it worked GREAT! I miss having my larger tank setup but I learn more about water quality with my Nano – so overall I think it’s better for me to be without one for the time being.

  • a HOB refugium might work for you little cube Jordan. 12G isn’t that big of an ocean liner…!

  • Daragh…usually biopellets and phos reactors aren’t run together. The refugium could still be run although you probably won’t see much algae growth as the biopellet reactor will get your tank to ultra low nutrient state. The fuge would still make for a good pod farm tho!

  • chris…the rock is really just for biological filtration. You’ll get some dead spots, but i’m ok with that has detritus gets stuck in the dead spots and when I do my water change, I move the rocks around and suck up the detritus.

  • Nice that you have the space to put in a big fuge Studio!

  • Bob…I think turf scrubbers are great but I don’t have the space to run one.

  • Devin…part of photosynthesis is a dark period of no light. So I like to obey my nature’s rules and turn off my fuge lights during the day

  • Khurram says:

    Hi mark, I have my refugium setup the way you have, do I need to trim the algae I have a mixture just like yours, or should I leave it be. It is covering the entire surface of my algae section
    Also I ordered a few things from vivid aquariums , got It today, great healthy stuff.

  • Kim93 says:

    How about Algae Turf Scrubber(ATS),ever heard it before?

  • William says:

    Hey Mark, I just wanted to say my fuge is doing an excellent job on my 125, I am using a 75 gallon tank for my sump with about 50% dedicated to a DSB and fuge. My phosphates, and nitrates have been staying at or close to 0 since it was set up. Some of my salt water friends thought I was crazy for making such a large sump but it’s doing the job. Thanks for the great site, and looking forward to hearing more about your LED trial.

  • Darvin L Pack says:

    Ok I have To ask..
    You say the alage goes sexual..
    I have know ideal what you mean by this??
    I run this alage in my sump…..

  • Devin says:

    Thanks for answering my question…I forgot to add one important factor. At this time I don’t have a display light (low on $$), but I plan on purchasing it within the next month or two. So currently I have a FO tank, and besides the ceiling lights the fuge light is the only light that’s hitting the tank thus the reasoning for the lights being on 24/7. If your advice is still the same and not having my display light matters then I will switch to the fuge lights only running during the night.


  • Mad Hatter Reef says:

    This is a great subject. I kinda surprised that is video didnt spark a debate because It seems to me that refugiums are one of those subjects that every hobbyist has thier own way of doing things. As for myself one of the biggest down falls of Macro Algae is “when” it dies, it releases nutritents and organic matter(what you were trying to get out of your tank) into the tank. When using Refugiums we need to keep in mind that in most cases our tanks are closed systems. Nutritents, Organic Matter and Detritus doesn’t leave the tank unless it’s removed from the tank by the Hobbyist (for example Water Changes and Skimming). I’ll stop now… LOL. Great subject Mark. Cheers.

  • Jin says:

    when you talked about the lights ??? did you meant PC flourecent lights or PC sun light cuz here at home depos they dont have Kelvins on ANY of the lamps and how can i cover the lamp cuz if a drop of water accidently gits it it will explode . plz answer mark my man

  • Chris says:

    1.My ulva went sexual when I threw I first threw it in my fuge. My seahare ate it up, and that’s that.

    2. Good point on the flow rate. Macro is like carbon, and needs a long contact time to pull out nitrates and phosphates.

    3. As of this year… your state is one of those that prohibits (most) calaurpa. C. ashmeadi, racemosa (all forms of grape), and of course taxifolia, are all illegal. Just thought I would give you a heads up. They outlawed almost 1/3 of all the freshwater ornamental plants, but added a few key saltwater species to the list.

  • Jonathan Peyton says:

    75g tank 55g sump 18g of that is fuge.

    Cheato ball the size f basketball.Soaks up all the Phos before I can measure it.Live rock amphipods and copepods galore.

    I love it .Its almost as fun to watch s the display tank

  • Jonathan…that’s a nice size fuge!

  • Mark F says:

    Mark, I have a 60 gallon remoter fuge with sand. I am debating removing the sand but, there is a lot to be said for having a sand bed that has lot’s of worms, etc. as part of the diversity of the tank and also having a anoexic area for nitrate removal.

  • I’m not a fan of deep sand beds, but if it is in place in your fuge, I’d let it be.

  • Ben says:

    I have a 125g fish tank with a separate 35g Fuge with and overflow to my skimmer section then to a sump/return. I control my flow to my fuge with a ball valve. My fuge started out a year ago with just a small ball of calaurpa. It now has a good watermelon size of it. I also trim it and feed my two tangs a Sailfin and Chocolate Mimic. They gobble it up in no time what so ever. This is a good way to ensure control of it and a good feed for tangs.

  • Landon Tucker says:

    Mark, what do you think about having a 30 gallon refugium for a 55 gallon display aquarium, because that is my setup. It also has a 3 inch dsb and run a light that is very close to yours.

  • Calireefer says:

    Mark, not sure what you mean by “you don’t have room to run an Algae Turf Scrubber”. Looking at your sump I can see a couple routes you could go and fit fine in your sump. A refugium is good but an Algae Turf Scrubber is like a super charged refugium (10x the filtering power in the same size space). I think an ATS does the same for a refugium as a Reactor does for GFO, it super charges the media and makes it work better, with the ATS making the algae work at its peak efficiency instead of in a refugium where only the top of the algae gets light and the stuff below is dark. The only reason I can see someone not using an ATS is they can’t clean them on time (weekly) as required, if you know you can’t clean it as required, no point in going that route because it will end up doing more harm than good and a refugium would be a better choice.

    Love your site and videos! Best there is IMO for our hobby. Keep up the fantastic work!

  • thanks for the nod about the videos/site!

    I figure I have room for the scrubber but not the lights to go over/on the side of it. Right now my sump is nice and open and I feel like a scrubber would clutter it up.

    I’m not against ATS as I think they are great ideas, but I’m not going to try to set one up at this point.

  • Calireefer says:

    Well said, and it is your tank and only you know what is best for it. I certainly don’t push methods on others, just like to post information on the different methods so people can make the most informed decision for their setup. A refugium is a tried and true method for sure, and I had great success for years with an inline refugium like you posted (middle chamber) stuffed with caulerpa so a refugium is certainly a good method as long as it is sized properly.

    I am using LEDs on one of my scrubbers and now using 20 3w Osram 660nm Red LEDs that RapidLED sells after doing experiments with every type of 3w Cree LED to see which ones grow algae the best. Answer: None of the Cree’s work well for algae, great for displays though. The 660nm LEDs do seem to grow algae the best by far, double the growth of any type of Cree white led, and blue LEDs do not grow algae at all. I use 10 LEDs per side on a full size screen (13″x10″). Just responding to your lighting/clutter issue you said, which I certainly see your point if using CFL bulbs + Reflectors, so just throwing out alternatives for you to think about for later down the road if you are ever thinking of trying one yourself.

  • Scott A. says:

    You can also look at the SantaMonica 100, which is an awesome 3d type acrylic turf scrubber. It’s around$700, but it’s clean and easy to incorporate. Not neccesarily for you Mark, but anyone who is reading this. I got mine for my 210 and it’s a real nice well built piece of equipment.

  • Heard of that brand. Most ATS I’ve seen are DIY projects as making one is pretty easy.

  • Byron says:

    Great topic Mark. I like the way you alternate the display tank lights with the refugium lights during day and night.

  • jon says:

    hey mark just wondering is it ok to run a uv srerlizer in my salttank with fish only,and a rufugium with kado alga


  • John says:

    Hey mark what do you think of in tank refuges and im more into growing food for my fish. wont the return pump cut up all the criters im trying to grow for my fish if its in my sump. im not worried about my refuge taking care of nitrates and so one my tank will do that but i would love to have a natural food source to keep my fish happy and health. thanks

  • sky says:

    Great video,

    What is your opinion of caulerpa in sps displays? I have heard caulerpa produces toxins that harm sps, specifically when it is broken such as when fish eat it.

    Is there a reason you only covered grape caulerpa as instead of others(such as the bladed or feathered)?

  • John…personally Im not a fan of macro algae in my display tank, but that’s just me., If your fish enjoy munching on the algae, you probably won’t be able to grow enough, fast enough before your fish graze it all down to nothing. That’s part of the idea behind a refugium: a safe place away from predators to grow critters and algae.

    And yes, some critters will get chopped up in your return pump and some will make it through.

  • Mike Byrnes says:

    Hey Mark, I’m looking at investing in a fuge/sump, but don’t have a lot of room under my tank because it’s split in half by a support plank.

    Tank is 65, It’d be about a 30g sump/refuge with 15g for sump/skimmer and 15g fuge for sand bed, rock rubble and calaurpa.

    Do you think that’ll keep phosphate and nitrate levels stable or is it too small compared to the 65 display to make a difference? I’m not looking to invest if it doesn’t have a positive impact.

  • I don’t know whether it’s my caulerpa racemosa turning sexual but since I have introduced them to my refugium my protein skimmer has turned crazy. I am wondering if this is the case then I should be ready for nitrates and phosphates boost. Any comments on controlling these effects or should I get rid of that algae?

  • Kenneth Sanchez says:

    Hey Mark,

    I have a 55g FOWLR tank. Would a 20g Refugium /Sump be large enough for my tank? What would you recommend?

  • Kenneth…that’s not a bad size for your 55g tank. If you have room for a bigger one, it can’t hurt!

  • travis krusell says:

    Hey Mark, I was wondering what your opinion is on ecosytems miracle mud. And have you ever used it?

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