Sound OFF: It's all about that FLOW that FLOW that FLOW!

[MnFish1]

This is the answer. There is no such thing as 'laminar flow' in a tank with objects in it. Every time a bit of water hits a rock - it disrupts the laminar flow - and by definition - its no longer laminar. Now - if you set a power head directly in front of a coral it would be hit by pure laminar flow - but it doesn't last long. Here is an interesting opinion from another article for those interested.

https://www.advancedaquarist.com/2006/11/aafeature/view?searchterm=water flow

PS - There was another thread/poll asking this same question -I forgot to answer this one. I use 2 Maxspect Gyres - in a 5 foot tank - with flow in one direction for 5 minutes - followed by flow in the other direction - alternating. I think "laminar" is better - but again - it doesn't stay laminar for long. PS- Divers- correct me if I'm wrong (I've snorkeled - and get this impression) - the flow naturally in the ocean is FAR higher than any flow we get from a pump in an aquarium (the way people usually use pumps - I know that sounds unmeasurable but just saying ) @Dana Riddle

 

[Dana Riddle]

I feel there is confusion between laminar flow, chaotic flow, and coral needs. There are many studies talking about how laminar flows do not penetrate the boundary layer of the interchange zone of the coral. Chaotic flow reduces that boundary layer providing better exchange of nutrients and wastes. This has someone come to be taken to mean that chaotic flow in the water of our systems is better then laminar flow. That isn't necessarily the case. IMO, reefers should be worried about velocity and velocity is better achieved with laminar flows. If you get enough velocity the flow becomes chaotic when it hits the coral and reduces the boundary level to allow better waste/nutrient export.
If you have chaotic flow away from the coral, your flows are intersecting and reducing the velocity before it hits the coral. The result is that you get lower velocity at the coral and that chaotic flow will move around the coral in a more laminar fashion. This is the opposite effect of what we want.
I do think many people who run "chaotic flow" in their tanks actually have multiple high velocity laminar zones and so they get good results. As the powerheads change speeds, these zones shift through the tank ensuring every coral gets the high velocity laminar flow it needs. So these good results may not be for the reasons they think.

I could be out to lunch... maybe we can get @Sallstrom or @Dana Riddle to weigh in.

I built a flume some years ago to investigate water velocities (as measured with a $5,000 digital velocity meter) on corals. The flume had flow straighteners so flow was definitely laminar (at least mostly so until it met the coral skeletons used in the procedures.) At the time of these experiments the best flow generators were small powerheads designed for use with under-gravel filters and detritus was removed manually, with turkey basters, waving of hands, etc. These skeletons were partially covered with detritus from an established aquarium and when velocities reached a critical point, the Bernoulli Principle was vividly demonstrated (this principle states as velocity increases, pressure decreases (and vice versa) - this is what keeps aircraft in the air.) In other words, the water rushing over the coral skeleton caused a pressure drop thus lifting detritus up and away from the skeletons. I suppose it is possible to have enough chaotic flow that would cleanse a skeleton in a similar manner but it personally believe it would have to be powerful. I published some of these results in Aquarium Frontiers in the mid/late 90's.

 

[Dana Riddle]

PS - There was another thread/poll asking this same question -I forgot to answer this one. I use 2 Maxspect Gyres - in a 5 foot tank - with flow in one direction for 5 minutes - followed by flow in the other direction - alternating. I think "laminar" is better - but again - it doesn't stay laminar for long. PS- Divers- correct me if I'm wrong (I've snorkeled - and get this impression) - the flow naturally in the ocean is FAR higher than any flow we get from a pump in an aquarium (the way people usually use pumps - I know that sounds unmeasurable but just saying ) @Dana Riddle

I just posted a reply when I saw your alert. Yes, you are correct - flow in the ocean can be intense. Even at a sheltered Hawaiian beach (Kahaluu, Big Island), sensors I had cabled tied to 5 pound dive weights could get tossed around. Kahaluu is also called 'Childrens' Beach' because it is sheltered from strong wave action by the famous Menehune Stone Wall.

 

[Brew12]

I built a flume some years ago to investigate water velocities (as measured with a $5,000 digital velocity meter) on corals. The flume had flow straighteners so flow was definitely laminar (at least mostly so until it met the coral skeletons used in the procedures.) At the time of these experiments the best flow generators were small powerheads designed for use with under-gravel filters and detritus was removed manually, with turkey basters, waving of hands, etc. These skeletons were partially covered with detritus from an established aquarium and when velocities reached a critical point, the Bernoulli Principle was vividly demonstrated (this principle states as velocity increases, pressure decreases (and vice versa) - this is what keeps aircraft in the air.) In other words, the water rushing over the coral skeleton caused a pressure drop thus lifting detritus up and away from the skeletons. I suppose it is possible to have enough chaotic flow that would cleanse a skeleton in a similar manner but it personally believe it would have to be powerful. I published some of these results in Aquarium Frontiers in the mid/late 90's.

Thank you Dana. I very much appreciate all the research you have done and that you are willing to share your opinion with us. The generosity you show with your time has been very helpful to me personally.

 

[MnFish1]

Thank you Dana. I very much appreciate all the research you have done and that you are willing to share your opinion with us. The generosity you show with your time has been very helpful to me personally.

Yes - thanks a lot - invaluable!

 

[Lostreefin]

I shoot for maximum chaotic flow. If the surface of the water isn't rippling in all different directions and sediment isn't getting stirred up in the sand bed I'm not satisfied.

 

[redfishbluefish]

Great to see Dana jumping into the fray. I can't begin to tell you how many times I've posted his 2016 MACNA talk...that included how flow impacts growth/photosynthesis.

Anyway, I'm now wondering if the debate here is a matter of definition. When I talk laminar or turbulent flow, I'm thinking fluid dynamics...flow velocities. I've just read all posts and I've got to believe that some are commenting from settings on powerheads. I say this because some stated they prefer "turbulent laminar flow." I'm not up on newer equipment, so with ignorance, is that a setting on some powerheads. The reason is that this is like saying I like hot cold showers. It's either laminar flow or turbulent flow (chaotic). Yes, it could be laminar until certain velocities or impacting rock/coral/walls or other flows from other powerheads. Let me finish by stating that the fastest growing magnificent tank of sticks that I've seen from our local club is from a member who had a 180 gallon with what we believed were 12 powerheads. The owner didn't actually know how many, so we counted and found at least 12. Flow, flow and more flow all over the place in a chaotic mess of very large colonies of sticks!

 

[MnFish1]

Great to see Dana jumping into the fray. I can't begin to tell you how many times I've posted his 2016 MACNA talk...that included how flow impacts growth/photosynthesis.

Anyway, I'm now wondering if the debate here is a matter of definition. When I talk laminar or turbulent flow, I'm thinking fluid dynamics...flow velocities. I've just read all posts and I've got to believe that some are commenting from settings on powerheads. I say this because some stated they prefer "turbulent laminar flow." I'm not up on newer equipment, so with ignorance, is that a setting on some powerheads. The reason is that this is like saying I like hot cold showers. It's either laminar flow or turbulent flow (chaotic). Yes, it could be laminar until certain velocities or impacting rock/coral/walls or other flows from other powerheads. Let me finish by stating that the fastest growing magnificent tank of sticks that I've seen from our local club is from a member who had a 180 gallon with what we believed were 12 powerheads. The owner didn't actually know how many, so we counted and found at least 12. Flow, flow and more flow all over the place in a chaotic mess of very large colonies of sticks!

To me this translates into - there is no such thing as chaotic /pure laminar flow. The key (to me) is high flow - across every piece of coral.

 

[chefjpaul]

To me this translates into - there is no such thing as chaotic /pure laminar flow. The key (to me) is high flow - across every piece of coral.

Yes-
To your diving question, that is how it feels.
Obviously different per region and even reefs within a region, but regardless, it's strong.

Iets use the mesoamerican barrier reef. In Cozumel its a very strong turbulent "drift" style current. Down in Belize it feels calm comparatively, but its way more unpredictably random.

The structures play an intriguing part, as this is where the chaos terminology comes to play.

In Cozumel, they're larger patchy reefs closer together with large sand beds leading to massive walls = high flow drifting.
Belize has more smaller patches randomly, leading to channel style structures = more random, drifting to calm in a relatively small area. But both still strong, yet different based on the structures creating different "chaos".

Now on the GBR, that's a different platform.

On every reef, nothing really takes a break and everything is moving, sometimes subtly, sometimes it looks like corals are going to just get torn apart in a matter of seconds at times. underwater I just watch this in awe.

Crazy how much they take the high movement, yet we have to control a glass box via technology, and aquascape, where nature uses weather, structures and the moon very randomly.

I use 3 very different power heads in a 50 gallon tank creating a lot of movement. Best tank I have ever had. Not bring afraid of high flow, whereas prior I was vastly under.

Wish I had a moon to control my wave makers.

 

[Dana Riddle]

Great to see Dana jumping into the fray. I can't begin to tell you how many times I've posted his 2016 MACNA talk...that included how flow impacts growth/photosynthesis.

Anyway, I'm now wondering if the debate here is a matter of definition. When I talk laminar or turbulent flow, I'm thinking fluid dynamics...flow velocities. I've just read all posts and I've got to believe that some are commenting from settings on powerheads. I say this because some stated they prefer "turbulent laminar flow." I'm not up on newer equipment, so with ignorance, is that a setting on some powerheads. The reason is that this is like saying I like hot cold showers. It's either laminar flow or turbulent flow (chaotic). Yes, it could be laminar until certain velocities or impacting rock/coral/walls or other flows from other powerheads. Let me finish by stating that the fastest growing magnificent tank of sticks that I've seen from our local club is from a member who had a 180 gallon with what we believed were 12 powerheads. The owner didn't actually know how many, so we counted and found at least 12. Flow, flow and more flow all over the place in a chaotic mess of very large colonies of sticks!

I should note that the referenced MACNA presentation had a small Tunze powerhead creating laminar flow across relatively smooth Porites corals, and photosynthesis increased with increasing water velocity. Sure there was some turbulence downstream of the corals, but most flow was laminar. And I'll throw this into the mix:
https://www.advancedaquarist.com/2014/5/equipment
These tests were performed in a tank that was 8 feet long. The Marsh-McBirney digital velocity meter I used could detect velocity if the sensor wasn't pointed directly into the flow by showing a negative number. Also note the jet stream (not diffusing) velocity patterns created by these pumps.

 

[w2inc]

Yes-
To your diving question, that is how it feels.
Obviously different per region and even reefs within a region, but regardless, it's strong.

Iets use the mesoamerican barrier reef. In Cozumel its a very strong turbulent "drift" style current. Down in Belize it feels calm comparatively, but its way more unpredictably random.

The structures play an intriguing part, as this is where the chaos terminology comes to play.

In Cozumel, they're larger patchy reefs closer together with large sand beds leading to massive walls = high flow drifting.
Belize has more smaller patches randomly, leading to channel style structures = more random, drifting to calm in a relatively small area. But both still strong, yet different based on the structures creating different "chaos".

Now on the GBR, that's a different platform.

On every reef, nothing really takes a break and everything is moving, sometimes subtly, sometimes it looks like corals are going to just get torn apart in a matter of seconds at times. underwater I just watch this in awe.

Crazy how much they take the high movement, yet we have to control a glass box via technology, and aquascape, where nature uses weather, structures and the moon very randomly.

I use 3 very different power heads in a 50 gallon tank creating a lot of movement. Best tank I have ever had. Not bring afraid of high flow, whereas prior I was vastly under.

Wish I had a moon to control my wave makers.

Water flow at the great barrier reef. 9 months south, 3 months north. http://www.mrstevennewman.com/geo/GBR/Hydrological.htm

Source: http://www.marine.csiro.au/LeafletsFolder/37eac/

 

[Brew12]

Let me finish by stating that the fastest growing magnificent tank of sticks that I've seen from our local club is from a member who had a 180 gallon with what we believed were 12 powerheads. The owner didn't actually know how many, so we counted and found at least 12. Flow, flow and more flow all over the place in a chaotic mess of very large colonies of sticks!

This isn't contradictory to laminar flow being what is important. The owner created 12 localized areas of high velocity laminar flow. Very healthy for corals. Where the pump flows intersect and becomes chaotic, the velocity drops an becomes less useful.

It's not that pulsing or varying flow is bad for corals and doesn't have its benefits. Only that establishing laminar flows is the most efficient way to establish higher velocities.

 

[Rick.45cal]

You can have both, my tank has extremely high laminar flow so much so that it pushes all the water through the rock structure. But I also have where all the pumps responsible for producing the bulk of the laminar flow current (panta rhei pumps) are on simultaneously so the streams all intersect creating very strong chaotic flow. The pumps on each side of the tank cycle on and off at differing intervals so what is created is a “rolling wave”(for lack of a better term) of very strong turbulent water that moves across the tank as the opposing pumps come on. (Since the pumps on one side cycle on at a slightly different interval the “turbulent wave” is constantly changing in duration and which side of the tank it starts at).

 

[Dr. Dendrostein]

You can have both, my tank has extremely high laminar flow so much so that it pushes all the water through the rock structure. But I also have where all the pumps responsible for producing the bulk of the laminar flow current (panta rhei pumps) are on simultaneously so the streams all intersect creating very strong chaotic flow. The pumps on each side of the tank cycle on and off at differing intervals so what is created is a “rolling wave”(for lack of a better term) of very strong turbulent water that moves across the tank as the opposing pumps come on. (Since the pumps on one side cycle on at a slightly different interval the “turbulent wave” is constantly changing in duration and which side of the tank it starts at).

When you wrote that, i thought he solved the issue of two masses occupying the same space. How did you solve that?.

You knw im yanking your chain

 

[Lukas75]

C) All of the above

But if I absolutely had to choose I would say laminar, but alternating from one side of the tank or the other throughout the day.

 

[WVNed]

After a year of running gyres I am sticking PP-8s in the tank too running 100%. I am fighting stuff settling on my corals and gorgonians.
The gyres wont blow it off no matter how high I turn them up.

 

[MnFish1]

After a year of running gyres I am sticking PP-8s in the tank too running 100%. I am fighting stuff settling on my corals and gorgonians.
The gyres wont blow it off no matter how high I turn them up.

Curious - which gyres are you using - and how big is the tank. I literally can't run my gyres at anywhere near 100% (but they are the new F350's)...

 

[PicassoDan]

"You keep using that word. I don't think it means what you think it means..."

If you have anything above a slight movement of water in your tank, it's really all turbulent flow. Nothing in front of a powerhead can be accurately called laminar. I realize it's just terminology, but in this case it's bad terminology, and I wish we could get away from it.

Reynold's number is how you know:
Re <2300 - the flow is laminar
2300 < Re < 4000 - the flow is transient
4000 < Re - the flow is turbulent

To get Reynold's number above 4000 in a tank full of water, the water has to be moving a few millimeters per second. Yep, that slow. Pretty sure that's every powerhead and all tanks represented on this site.

 

[MnFish1]

"You keep using that word. I don't think it means what you think it means..."

If you have anything above a slight movement of water in your tank, it's really all turbulent flow. Nothing in front of a powerhead can be accurately called laminar. I realize it's just terminology, but in this case it's bad terminology, and I wish we could get away from it.

Reynold's number is how you know:
Re <2300 - the flow is laminar
2300 < Re < 4000 - the flow is transient
4000 < Re - the flow is turbulent

To get Reynold's number above 4000 in a tank full of water, the water has to be moving a few millimeters per second. Yep, that slow. Pretty sure that's every powerhead and all tanks represented on this site.

Correct me if im wrong - isn't this more useful in pipes? or tubes? - thats where it becomes more important. (ie the words laminar vs turbulent). Agree with you that except for maybe a couple cm in front of any pump the flow will be more turbulent.

 

[PicassoDan]

Definitely easier to understand in the context of pipes, but Reynold's number is used in all kinds of fluid mechanics, including external flow - think airplanes, etc.
It's just every time I read about someone having laminar flow in their tank...

We really should be talking about the amount of turbulence, but I guess that's harder to quantify. Or we should talk about overall flow patterns, or maybe even water velocity.