- We all know that it's important
to have good flow in our reef tanks.
The rule of thumb that I see online a lot for flow
in an Acropora-dominated reef tank
is usually determined in terms of total tank turnover.
So how many times does the water volume
in your tank turn over in an hour?
World Wide Corals says they aim
for about a hundred times turnover in their SPS tanks.
Other folks I've seen online are more
in the 50 or 60x turnover range.
So that means if you have a nice hundred-gallon reef tank,
to make the math easy,
you should shoot for around 6,000 to maybe 10,000 gallons
per hour of flow from all of your pumps combined.
To be honest though,
this seems a little bit on the low side to me.
I have about a 280-gallon tank,
and if I were to run all of my pumps at a hundred percent,
I'd have nearly 37,000 gallons per hour of water flow.
And there is the issue.
Your pumps are rarely running
at a hundred percent of their actual capacity.
Hi guys and girls, I'm ReefMan.
And this week, we're talking about flow.
Why is it so important?
What difference does it make in a reef tank anyway?
Well, flow is critically important for corals.
It's how coral moves all the soluble chemicals and nutrients
between the water and its tissue.
More flow directly leads
to more nutrients being taken into the coral.
Water flow increases respiration
and the amount of oxygen that the coral gets.
In turn, that increases the rate of photosynthesis
that the coral can do.
Flow also regulates the introduction
of things like dissolved carbons
and things like that into the coral,
and all that is needed for growth,
for calcification, for photosynthesis.
Now I came across a really interesting paper recently.
It is titled, "Going with the flow:
how corals in high-flow environments can beat the heat."
There is a link down below in the description.
You should check it out yourself.
It's a really great paper.
And this paper helps to explain
not just how important flow is to our coral,
but why it's important from a genetic level.
Now this paper doesn't talk
in terms of gallons or liters per hour,
things that we would be more familiar with.
They're talking about water velocity,
centimeters per second.
Now, correct me if I'm wrong down below,
I'm sure you will,
but I think we can directly convert a centimeter per second
into a volume of water moving
so many centimeters in a second.
So, if that's true,
in the paper, they're studying corals growing
in a high-flow location on a reef in Guam,
and they're comparing them to corals
in a low-flow location on the same reef.
The high-flow location has water moving around
8 to 16 centimeters per second.
Doing some math with my tank,
which has an edge about 3 feet by 2 feet,
I think that works out to about 44,500 gallons per hour,
up to about 84,800 gallons per hour in my tank.
Now that's based on using the area of the side of my tank
and some equations usually used to calculate the velocity
of water flowing through a pipe.
So, it's an estimate,
but hopefully close enough to get some information from.
Now, in the paper,
the lowest flow was around half of that.
So, low flow in my 280-gallon tank
would be around 22,000 gallons per hour.
Now, I have six VorTech MP40s in my tank.
Each one, if they're at a hundred percent,
is about 6,000 gallons per hour,
and my return pump is about a thousand.
And so I have about 37,000 gallons per water,
or hour of water movement at the high side.
And so that's going to be on the very low end of flow
from the experiment.
My tank turns over 132 times an hour,
so that's more than a lot of tanks,
but nowhere near what the high-flow reefs
are actually seeing in the wild.
Okay, so now we know how to calculate the flow in our tanks
and we know where that will fall on the low to high flow
of at least Guam's reefs,
the ones studied in the paper.
What did they find?
Well, in short, the corals growing in the high-flow location
were much healthier.
Fewer of them died during recent bleaching events.
In fact, more than 80% of corals died in the low-flow area
and less than 20% died in the high-flow part of the reef.
So what gave the coral this increased bleaching resistance?
That is what they wanted to find out.
Now, it turns out water flow impacts which genes
are being expressed in the coral.
There's 120 genes that they found
which are expressed differently
in the high versus low flow areas of the reef.
Those genes are related to all sorts of things.
Everything from the motion of cilia, to glycolysis,
to amino acid synthesis, which is increased with more flow.
There are even genes that reduce oxidative stress,
which are upregulated when you increase the flow
that the coral's exposed to.
Some genes are even front-loaded.
That means they're upregulated
even when there is no environmental reason for them to be.
And it turns out that a lot of those front-loaded genes
are actually related to allowing the coral
to survive heat stress.
That means that these corals growing
in the high-flow location
are better equipped to survive the heat stress,
and that's the main cause of coral bleaching
around the world and certainly on that reef in Guam.
The effect of all of these changes in genes
is that corals growing in higher-flow locations
are better equipped for feeding.
They're better equipped to process the resulting nutrients
and amino acids that they get from the food.
They get more nutrition,
and the upregulation of genes
that are involved in nutrition transport
means that they can make better use
of the nutrition that they get.
Corals under higher flow actually bleach less,
and when they do bleach,
they recover a lot faster than corals in low-flow areas.
The study looked at corals in the wild
as well as the same corals grown in aquariums,
so those effects are not only seen in wild corals.
Maybe it's the time to add a new pumper to your tank.
In my tank, I'm really not sure that I could even come close
to doubling my flow in order to achieve the highest flows
that they measured on the reef in Guam.
But for sure I could add a Gyre or two
to the back corners of my tank,
and that's gonna increase the flow quite a bit
from where I am today.
It is hard to manage flow in an aquarium.
Corals grow, they block flow.
You need a strong flow,
but you can't just blast a coral day in and day out
because that'll kill it before any of the benefits
that we're talking about here could even take place.
Flow needs to be diffused and random,
yet overall strong enough to make a difference in your tank.
Pumps like VorTechs or the Gyre pumps
do have wide dispersion patterns to their flow,
and so you can get away with them
being closer to your coral.
You can also use dividers and things like that
on your returns from your return pump
to randomize the flow a bit more from that.
But really, don't stress too much
about the micro-optimizations you can make with your flow.
Just make sure that you have enough flow
to maybe be on the high end of what's recommended,
a hundred, maybe 150 times turnover in your tank
if you want to assure that you're at least
above the low flow that they were studying in the paper,
so that you can achieve some of those benefits.
I hope you found this as interesting as I did.
The paper is, as always, linked down below.
I do encourage you to check it out
if you want a lot more detail,
especially around the genetics that they did.
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and you enjoyed the video.
Be kind to each other.
Stay safe.
Have a fantastic day.
Bye.