- Anyone with a reef aquarium knows that good water flow
is key to having healthy corals and a beautiful tank.
Today, wanna take a look at why.
(upbeat music)
Hi, this is Wayland from Marine Depot
and thanks for tuning in.
In the early days of reef-keeping,
we had to use bulky power heads
to get the water moving in our tanks.
The flow pattern was all wrong
and we were blasting corals like a power washer.
Today, we've got compact cool-running flow pumps
and wave pumps that make recreating
reef-like water motion much easier.
But do you know the science behind the benefits
of water movement in nature and in our reef tanks?
We'll discuss the basics of water flow
and the benefits it brings to our aquariums as well
as we look at how it can benefit your corals specifically.
In nature, reefs are exposed
to many kinds of water movement.
The flow patterns range from steady, mild currents
to cyclic wave action.
Waves and tides constantly flush the reef,
washing away waste products
and bringing in nutrients and suspending plankton.
Since most of the reef's inhabitants are sessile,
meaning they don't swim or crawl around,
food, nutrients, gases and waste are managed
by currents and waves.
Without water movement, the reef ecosystem
would collapse into stagnation.
The same is true in our reef aquariums.
You can't rely on the filter's output to adequately
stir up a reef tank.
To understand why, we'll have to look
at industrial water treatment.
It is a well-known principle that suspended particles
will fall out of a solution in a low flow environment,
especially if there are baffles that further
slow down the flow.
That's the principle behind settling tanks
used to purify waste water.
Organic and inorganic particles like bacteria, algae
and mineral particles are heavier than water.
Gravity causes the solids to fall to the bottom of a tank
when water movement is low.
The same thing happens in a reef aquarium.
Rock work, corners of the aquarium,
and the filter sump create low flow zones,
allowing suspended debris to settle and collect as sludge.
You'll also see fine debris settle on
and behind live rock and even corals.
Low flow prevents debris from making its way
to the filter sock and other mechanical filter media.
Like it or not, a reef aquarium is an ideal settling tank
with plenty of low-flow areas that collect particles
of debris.
Here's the fluid dynamics formula.
But you don't need to do the math
to know that sludge happens in an aquarium.
Reversing your reef's tendency to act
as a sludge collector is easy.
No matter what size tank you've got,
there's a flow pump made for it.
Increasing water movement will keep the debris suspended
so the filter can remove it.
But water flow is more than just keeping your tank clean.
So far, we've only looked at
the physical aspects of water movement.
Most of the marine life in an aquarium are microscopic.
You can't see them, but there are billions of microbes
at work to keep the ecosystem functioning.
While some of these microbes are in the water,
most are living on the surface in crevices of the live rock,
sand, and even form specialized communities
under coral colonies.
These micro environments range from oxygen-rich
aerobic zones on rock surfaces to anaerobic
denitrifying niches inside rock forms.
These colonies of microbes do most of the work
of purifying and recycling waste products
and also the nutrients in the aquarium.
But the fact is, they depend on water currents
to bring them the substances they need to do their job.
Think of reef rock and sand as a big biological filter.
It needs water circulation
to keep it functioning efficiently.
Circulation pumps bring the water to the rock
and flush away waste materials and sediments
that could interfere with the microbes
living on and in the rock.
Solid surfaces like reef rock,
even though they're submerged,
have a special thin layer of water
right at the rock-water interface.
This is called the boundary layer.
It's a thin layer of water that essentially does not move.
Fish, macro algae, and even corals are all surrounded
by a boundary layer.
Oxygen, CO2, waste, and other nutrients
have to pass through the boundary layer.
The lower the flow, the thicker the boundary layer.
Wave makers and flow pumps force water across the rock,
reducing the boundary layer and making it easier
for the microbes to do their job purifying the water.
In the earliest days of reef keeping,
marine biologists recognized that captive corals
did much better when there were wave-like currents
in the holding tanks.
We've known for a long time that corals in nature
are surrounded by a one to two millimeter diffusive
boundary layer, or DBL.
Water motion keeps the layer thin,
allowing easier transfer of nutrients and waste.
To mimic wave action, Doctor Walter Adey and others
experimented with surge tanks and dump buckets,
pioneering the way for today's modern
wave-making flow pumps.
Zooxanthellae algae inside the coral tissue
work with the coral pods to share energy-rich substances
and recycle nutrients.
Corals rely on water currents to bring food
and essential elements for many
biologically necessary processes.
These processes include photosynthesis by zooxanthellae,
carbonous skeleton building,
reproduction, and nutrient and dissolved gas exchange.
There are a number of studies that show coral metabolism
as measured through photosynthesis and calcium carbon
production is directly affected by water flow.
The research is conclusive that slow water flow
inhibits coral growth.
But there's more than just a DBL at work here.
An international team of researches
discovered that corals just don't passively wait
for water currents to overcome the boundary layer.
The research revealed that reef-building corals
are covered with microscopic cilia
that constantly beat, creating mini vortices
that spin in the opposite direction of water flow.
Corals actively disrupt the boundary layer,
increasing transfer of nutrients to the coral,
and waste products out, by up to 400%.
That test was run in a tank containing
acropora, montipora, seriatopora, protopalythoa,
palythoa, and an opalytha discosoma.
These findings show how important water flow is
to the metabolic processes of corals.
Corals need water flow to maximize growth and health.
Coral cilia can influence a boundary layer
but only up to about two millimeters from their surfaces.
Increasing water flow is essential to bring
the boundary layer down to one to two millimeters
so corals can manage the nutrients and gases
that affect growth.
Increased flow also maximizes a micro community's ability
to remove nitrate ammonia and other waste.
And finally, a flow pump will keep debris
from collecting behind a live rock.
Wave makers and flow pumps do more than make coral sway
like they do on a reef.
Water flow is an integral part of the coral biology
and necessary for keeping corals in captivity.
We no longer need to build our own surge device
to have great flow for our corals.
Today, we have an array of purpose-built water pumps,
many with tide and wave mimicking functions
built right in.
No matter what size of reef you have,
there's a flow pump for you.
We hope you found this information helpful.
If you did, let us know by clicking the like button below
and feel free to share it with your friends.
Until next time, take care and happy reef keeping.
(upbeat music)