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You are here: Home / Refugium Education / Water Flow in the Refugium
Refugiums are great for Marine Aquarium Health

Water Flow in the Refugium

by greg.chernoff

When it comes to setting up your refugium, there are plenty of considerations to make. You must select macroalgae species, clean-up crew species, a type of substrate (or none?), lighting and so on. Most of this planning is pretty fun. But, with so much to think about, and so many options, it might be easy to overlook one of the most important factors of all: water flow.

Water flow characteristics can significantly impact macroalgal growth rates and, therefore, the refugium’s overall capacity for nutrient export. And controlling dissolved nutrient levels is one of the main reasons for installing a refugium in the first place, right?

Types of Water Flow

The first distinction aquarists typically make when discussing water currents is whether they are chaotic or laminar. Chaotic flows are most like those encountered over shallow reefs that are subjected to strong wave action. As the term suggests, chaotic flows are highly inconsistent with regards to direction and velocity. Laminar flows are more like those in rivers and estuaries, as flow direction and velocity are more or less constant (they may change direction with the tides, but are nevertheless comparatively stable and predictable).

[Refugium]

So what does this look like in a refugium? A chaotic flow pattern might be created with the use of specialized water pumps. Usually controllable to some degree, these pumps can be adjusted for variable output, for movement (of the nozzle or the entire unit), or for both. In creating chaotic water movement, it might help to place the inlet from the main tank in the center of the refugium so that it may progress in all directions.

Laminar flows are a little more straightforward to create. In this case, you’ll want to direct the inlet to the far end of the refugium opposite the outlet. The water will simply flow from one side of the refugium to the other. Generally, for generating laminar flow, supplementary pumps are not necessary.

Which to Use?

Type of flow is usually dictated by the kind of macroalgae to be kept. Velocity can be higher for rigid forms (e.g. Chaetomorpha), but must be subdued for softer, fleshier types (e.g. Ulva). In more special circumstances, this will also be additionally influenced by the type of animals that might be housed there. For example, when using a refugium as a place to keep seahorses, a relatively gentle, laminar flow is ideal.

Most seaweeds will grow either attached or unattached. But, many prefer to grow one way or the other. Laminar movement that flows through the crop are best for attached macroalgae. If the aquarist aims to cultivate types that form canopies (e.g. Ulva) or sheets (e.g. Chaetomorpha), laminar flows are likewise suggested. This is most easily accomplished with a longer refugium.

Chaotic flow can be used to tumble the macros and is highly effective with unattached macroalgae. This is most easily accomplished with a taller refugium. The reason for tumbling is that it is incredibly efficient, since all parts of every plant receive light. These kinds of currents are most appropriate for compact, globular macros that don’t readily form canopies or big, solid masses (e.g. Gracilaria and Halymenia). Lighter, fleshier algae such as ogo require only a moderate flow rate, whereas heavier, denser algae such as leafy sphere appreciate something more vigorous.

How much flow is enough flow? Really, if our primary purpose is to remove nutrients, the higher the turnover of water through the refugium, the better. There are, however, some physiological limitations here. First of all, there will be some maximum efficiency at which the macros are capable of taking up the nutrients. And then there are also physical limitations to how much flow can be applied. This is because the more delicate types like Ulva and ogo can be damaged from shearing or compaction in the face of strong currents.

If one chooses a softer macro (maybe because the intent is to feed harvested material to herbivorous livestock), an “oversized” refugium is a good idea. Why? Because you can pass more water through it even at a reduced velocity!

Settling Things

There is an interesting caveat to the more-is-better rule for velocity. In terms of nutrient sequestration, yes, you want an overall faster flow. Still, it is quite desirable to have small pockets of lesser flow here and there. The reason for this is that it allows suspended particulate matter to settle out onto the bottom of the refugium. This accomplishes two things. For one, it reduces detritus build-up in the display tank (where you really don’t want to see it). Secondly, this deposits it right where your sludge-eating bacteria (e.g. PNS Probio™) and detritivorous harpacticoid copepods will be most abundant.

The macros themselves help with this. Friction slows water currents as they hit the plant surfaces. But one can fiddle around with baffles, the rockwork, pump orientation and so on to maximize settling.

Going With the Flow

No two refugia are exactly the same. A single refugium might even change considerably between growth/harvest cycles, as it biologically develops, etc. Therefore, unfortunately, there is no handy formula for the perfect flow pattern. But with some awareness of how water movement affects macroalgae growth (nutrient sequestration rates!), any aquarist can make adjustments as needed to get the most out of their planted refugium.

[Refugium]

Reader Interactions

Comments

  1. tdlawdo says

    March 4, 2019 at 9:25 pm

    I cannot get my chaetomorpha to grow.

    Reply
  2. Robert Blevins says

    March 29, 2019 at 4:40 pm

    I think less flow through the fuge is best for several reasons.

    Reply
    • Gary says

      May 6, 2019 at 3:23 pm

      Me also

      Reply
    • Edwin Boston Jr. says

      May 6, 2019 at 5:37 pm

      I have a medium flow and it keep things in really good shape.

      Reply
  3. billymumford0 says

    April 30, 2019 at 7:01 am

    Always wanted information on this topic.

    Reply
  4. Julia Burr says

    May 6, 2019 at 3:27 pm

    Thank you

    Reply
  5. Elmer says

    May 6, 2019 at 3:35 pm

    Nice info

    Reply
  6. Tracy Schultz says

    May 6, 2019 at 3:39 pm

    Great info here…

    Reply
  7. Rolando Llamas says

    May 6, 2019 at 3:43 pm

    This is information you don’t want to miss out on

    Reply
  8. seitzjh says

    May 6, 2019 at 3:52 pm

    I run a slow flow

    Reply
  9. Kenta Asazu says

    May 6, 2019 at 3:54 pm

    Cool!!

    Reply
  10. ponygirl112 says

    May 6, 2019 at 4:24 pm

    Awesome info thank you

    Reply
  11. brennanlottes says

    May 6, 2019 at 5:28 pm

    I have mocha ogo in my fuge and a spray bar for flow

    Reply
  12. Rhonda L Swetnam says

    May 6, 2019 at 5:47 pm

    Thank you! This article was very helpful!

    Reply
  13. Manuel A Ferro says

    May 6, 2019 at 6:04 pm

    I love my Refugium setup

    Reply
  14. Charles Wheeler says

    May 6, 2019 at 6:07 pm

    Great info!

    Reply
  15. Chad Sosby says

    May 6, 2019 at 7:44 pm

    My mandarin that I got from you guys would eat anything.

    Reply
  16. Tanya BAZALDUA says

    May 7, 2019 at 4:46 am

    Very good info

    Reply
  17. Jon Andrianos says

    May 7, 2019 at 4:56 am

    Very helpful!

    Reply
  18. Leslie Pustilnik says

    May 7, 2019 at 5:45 am

    Low flow in my fuge as well.

    Reply
  19. Richard Quickley says

    May 7, 2019 at 6:27 am

    I have my top off pumping into the return section

    Reply
  20. koon_kelly says

    May 7, 2019 at 8:36 am

    Good info!

    Reply
  21. Rudy Brambier says

    May 7, 2019 at 8:44 am

    With proper use of wave makers or circulation pumps in the display tank you can lower the flow threw your refugium to maximize your filtration.

    Reply
    • kevtide says

      August 24, 2019 at 7:41 pm

      I’m not sure I’m following. When you say lower the flow through your refugium, does this imply that you ramp down your return pump speed and increase display tank flow through the use of wave makers, etc?

      Reply
  22. Christopher Burns says

    May 7, 2019 at 10:31 am

    I might buy a HOB fuge

    Reply
  23. Chris G. says

    May 7, 2019 at 11:44 am

    great info

    Reply
  24. jordan16leblanc says

    May 7, 2019 at 7:48 pm

    Good to know

    Reply
  25. jamesdylanmccraw says

    May 7, 2019 at 9:22 pm

    Now my pods won’t be swept away

    Reply
  26. jamesdylanmccraw says

    May 7, 2019 at 9:22 pm

    Now my pods won’t be swept away

    Reply
  27. Robert says

    May 8, 2019 at 12:05 am

    got rid of cheato got some sea lettuce love it

    Reply
  28. Robert says

    May 8, 2019 at 12:06 am

    my fuge suck eshopps cube dont like it

    Reply
  29. Robert says

    May 8, 2019 at 12:09 am

    nice

    Reply
  30. Robert says

    May 8, 2019 at 12:10 am

    excellent

    Reply
  31. Menerd The Menace says

    May 8, 2019 at 3:20 pm

    Good read

    Reply
  32. Ricky J Gronwall says

    May 9, 2019 at 7:19 am

    These are great tips. Haven’t had a fuge in a while but setting up another soon!

    Reply
  33. Jack Goldstein says

    May 12, 2019 at 6:15 pm

    My caulerpa has definitely grown faster since I added a small powerhead.

    Reply
  34. Jordan Preston says

    May 12, 2019 at 11:26 pm

    I would say medium flow is best.

    Reply
  35. Wesley Paulson says

    May 13, 2019 at 4:30 pm

    Very Informative

    Reply
  36. Ken Ishiki says

    May 13, 2019 at 4:36 pm

    a slow tumble works best in for chaeto

    Reply
  37. Victoria Brewer says

    May 13, 2019 at 4:54 pm

    Great info I’ll have to try playing around with the flow to see if it affects growth

    Reply
  38. Douglas Campbell says

    May 14, 2019 at 6:39 am

    This info is absolutely amazing for the new hobbyist and for the experienced one as well just need to take the time to read and apply the information

    Reply
  39. Adrien says

    May 14, 2019 at 2:43 pm

    This helped me set my refuge up easily

    Reply
  40. Hardguyy says

    May 20, 2019 at 3:41 pm

    cool

    Reply
  41. Jonathon Berry says

    May 20, 2019 at 4:46 pm

    Great info thx

    Reply
  42. Savoury Kem says

    May 20, 2019 at 6:37 pm

    Interesting

    Reply
  43. Mike !! says

    May 20, 2019 at 7:06 pm

    Great info, thanks!!

    Reply
  44. Diana Aliprandi says

    May 20, 2019 at 7:13 pm

    Thanks for the article. There’s so much stuff to learn about the refugium

    Reply
  45. Compy Ginorio says

    May 20, 2019 at 7:17 pm

    Great reading, very helpful.

    Reply
  46. Carol Mauch says

    May 20, 2019 at 11:24 pm

    Liked the information about the MA in regards to the amount of flow different kinds prefer. Fun to learn new things to add to the basics.

    Reply
  47. Kevin R Gravier says

    May 21, 2019 at 12:19 am

    I appreciate the good info to take into account for the many facets of making a successful refugium.

    Reply
  48. Dwayne Newell says

    May 21, 2019 at 1:46 pm

    Turning up my return pump has force more water to circulate through the refugium allowing the Chaeto to take off

    Reply
  49. Krish says

    May 21, 2019 at 10:21 pm

    I have to add more flow to mine. Great read

    Reply
  50. Jose Ponciano says

    May 27, 2019 at 11:41 am

    So do I need a wave maker I. The refuge??? But flow is very important..

    Reply
  51. Robert Vice says

    May 27, 2019 at 5:07 pm

    maybe I need more flow I use the eshopps adv series and half the water goes through the fuge unfiltered and the other half goes to the skimmer after passing through the sock just switched to sea lettuce and its growing good

    Reply
  52. mcc says

    May 28, 2019 at 9:47 pm

    Good information. I’m interested in building a display refugium.

    Reply
  53. Jorge says

    May 29, 2019 at 10:14 pm

    I wish there was more advice for HOB refugiums

    Reply
  54. Nelly Acevedo says

    June 3, 2019 at 11:24 am

    Thanks great information

    Reply
  55. Alyssa says

    June 3, 2019 at 2:04 pm

    I didn’t even take this under consideration. Good read

    Reply
  56. Andrew B says

    June 3, 2019 at 4:26 pm

    Never knew this about my flow!

    Reply
  57. chris head says

    June 3, 2019 at 4:37 pm

    Flow rules!!!!

    Reply
  58. Danny DJ says

    June 3, 2019 at 4:44 pm

    Still battling if an external algae scrubber is better than a refugium. I think I’m going with the scrubber tho. Thanks for the information.

    Reply
  59. Tricia B says

    June 3, 2019 at 4:46 pm

    Great page!

    Reply
  60. Kris Kasarda says

    June 3, 2019 at 5:04 pm

    Great post!

    Reply
  61. cgault99 says

    June 3, 2019 at 5:23 pm

    Thank you

    Reply
  62. Andrew says

    June 3, 2019 at 6:15 pm

    I liked it

    Reply
  63. Nick says

    June 3, 2019 at 6:34 pm

    Thank you

    Reply
  64. Carrie Harvey says

    June 3, 2019 at 7:28 pm

    Good red thanks

    Reply
  65. Kenneth Showman says

    June 3, 2019 at 9:52 pm

    I found a lot of valuable information in these articles to consider when I get my refugium up and running. I know my refugium will be a better success because of the willingness to help educate the reefing community. As always the Algae Barn has the best high quality products with the right knowledge to go with them.

    Reply
  66. Garrett says

    June 16, 2019 at 2:49 pm

    Great information, I have Laminar flow through my sump. Where the water passes through a battle into the refugium is where I placed my Chaeto, so all the water passes straight through the macro. I have seen great growth after moving it into the direct current of flow. It used to sit tucked in the corner opposite the water baffle and wasnt receiving much flow. I wasnt getting much growth either. Now it seems to be loving the new location. I have it placed as some would use filter floss or pads.

    Reply
  67. William says

    July 23, 2019 at 8:42 pm

    Can anyone recommend an ideal water flow rate (gph) for both chaeto and sea lettuce in the same refugium?

    Reply
  68. Ed says

    July 11, 2020 at 12:25 pm

    Very interesting, thanks for this info here. I’ve run a hob fuge with a dsb on a 90 gallon reef years ago & it worked great. I’m getting back into the hobby & going nano with the Fluval Sea Evo 13.5. I have a small CPR refugium going to hang on the back, now I think I’ll try using the tanks built in mini sump for faster flow macros, live rock, etc & the cpr hang on I plan on a very slow flow using a continuous siphon instead of any extra pump for it & that will flow through miracle mud with some mangroves. I also have a mini skimmer but I don’t really think I’ll need to use it with this set up.

    Reply

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