I think that I can safely say that the movement of water in an aquarium is
one of the most disregarded, yet important, aspects of successful aquaria.
If you havenít ever really given it any direct thought before now, you
might be wondering what Iím talking about. Letís see if I can help you
understand its importance, and then weíll talk about some ways that you
can create healthy movement of the water in your fish tank.
The movement of water performs several vital functions. First of all,
it prevents thermal layering. Ever been swimming in a lake? Notice how
cold it gets a few feet under the surface? Thatís because hot water rises
and the colder water sinks to the bottom due to convection currents. With
current, you can mix the water so that there are no cold or warmer layers.
Second, water movement provides the fishes with a current in which to
swim. Before I began keeping African Cichlids, I had a 55-gallon tank
with various tetras. I had strong currents that were produced by power
filters. It was really interesting to watch them line up in front of one
of these currents and school in station for hours. It seemed that they
really enjoyed the current.
The third reason why water movement is beneficial is because it prevents
the formation of a protein film on the surface of the water. You may notice
this in your tank, or more obviously, on stagnant ponds or lakes. With
time, it can become thick and crusty. This film significantly inhibits
gaseous exchange between the water and the air. Are you beginning to understand
yet why water movement in your aquarium is so vital?
The next two reasons are perhaps the most important. By having your water
constantly moving, you increase the surface area of your tank. The layer
in contact with the air is always changing and consequently you dramatically
increase the rate at which oxygen can be dissolved into the water, and
carbon dioxide is released from the water. The surface area of your tank
is always the limiting factor in the number of fishes you can keep in
a tank. So, by artificially increasing your tankís surface area, your
tank is then able to house more fish.
The fifth reason why we should pay attention to water movement is because
moving water carries oxygen to the denitrifying bacteria in your tankís
substrate. Itís these bacteria that are responsible for the breakdown
of harmful waste products (i.e., ammonia and nitrite). Their breaking
down ammonia puts it into a form that allows your plants to use it (i.e.,
And most harmful bacteria are anaerobic. That means that they thrive best
in conditions with little to no oxygen. So, by providing a greater air
to water interface, you increase the concentration of oxygen in your water,
which both your fish and denitrifying bacteria need, and harmful bacteria
Now letís talk about how you can begin to create water movement in your
There are countless ways one could create water movement. What I will
do is share with you other approaches I've either seen or used that have
been effective. In implementing these methods, or in creating your own,
it is important to remember why we want current.
If you keep these goals in mind, you will know what method, or combination
of methods will work best for your tank.
- Prevent thermal layering
- Provide your fish a current in which to swim
- Prevent the formation of film on the surface
- Increase your water's surface area
- Increase the oxygenation of your water
The most common approach people take is to add an air stone to their aquarium.
This is often done with the belief that those bubbles will somehow cause
air to diffuse into the water. Sorry to bust your bubble, but air stones
are not going to directly increase the oxygenation of your water. What
they will do is disturb the surface of your water, and thus enable more
water to interact with the atmosphere.
For large tanks, a simple air stone will not do the trick. For small
tanks, like this 5-gallon tank here, it is probably the best approach
for creating water movement. For a small tank, you donít want to have
too strong of a current because the water will be like a fire hydrant.
Remember, you want to break the surface of your water to prevent the protein
film from forming and for increased surface area.
As I said, the use of air stones is the most common approach for creating
water movement, but is usually insufficient alone. The next most common
approach is to use an undergravel filter. This is supposed to create current
by pulling water through the gravel and out through the lift tubes. This
method relies upon the power of the rising bubbles in the lift tubes to
pull water through the gravel. This alone would hardly constitute an adequate
system for water flow. Maybe as a filter it works, but we're not talking
about filtration. We're talking about creating water movement.
I have seen two adaptations to Under Gravel Filters that seem to work
pretty well. One method is to put a power head on the lift tube to more
forcibly pull the water through the gravel and up the lift tubes. The
water is then redirected back into the tank in a stream. This stream can
be made more turbulent by introducing bubbles into the lift tube or power
The second method is to use MarineLand's Reverse Flow Kit. This works
by pushing the water through the gravel instead of pulling it. I think
the second method is best in terms of filtration, but if we keep our goals
in mind, we will realize that the first method is the best at creating
current. A concentrated stream of water near the top is going to disturb
the surface better than a diffuse current rising from the gravel. It will
also help circulate the water because it is pulling water directly from
the bottom of the tank and spitting it out at the top.
A few people use the Rio Duckbill Rotator. It attaches to most powerheads
and slowly rotates, distributing flow 360 degrees. This powerhead attachment
is useful because it changes up the current so that it is not always blowing
in one fixed direction. It is also very good at overcoming the problem
of "dead spots" in your tank. It also meets some of our other criteria
for a good water movement system by increasing the surface area of the
water and hence gas exchange.
The Sea Swirl by Aquarium Currents is also designed to eliminate "dead
spots" in the aquarium.
It works by oscillating your return line 90 degrees
every 60 seconds. Aquarium Currents has designed them specifically for
glass or acrylic tanks, and they come in 3 different sizes (Ĺ", ĺ", and
1"). They are designed to work with external pumps, although they could
be fitted to a submersible pump.These are a few examples of what is offered
commercially. What I find to be most fun, however, is to come up with
a system of your own. Really be engineering; dream up your own system.
I'll show you a few examples of what I have used in the past, or still
By having a spray bar, you can create a nice, directional current, and
disturb the surface of your water with the return line. You can adjust
the strength of the current by the size of the holes drilled in the PVC.
The smaller the holes, and the fewer of them, the stronger the current
will be. With this particular setup, I had the PVC just below the surface
of the water, angled horizontally.
What I prefer to do now is have the PVC above the surface of the water
and have it shower the water down, as if it were raining. It is not as
effective at creating a significant current but is effective at breaking
up the surface. I made the holes in my PVC to be pretty small so that
the shower does a good job of breaking up the water. This picture below
is of the top portion of my tank, and you can see the shower penetrating
a couple of inches into the water.