Throughout the 1980's the privately owned research and development
facility of Global Aquatics, located in Aberdeen, Maryland searched for
ways to grow fish in a profitable manner.
Like so many others back in that day, our first approach was to start
out with ponds to grow catfish and stripped bass.
After operating our ten acres of ponds for a couple of years we realized
this was not going to be a practical solution to solving the worlds need
for a new seafood source.
The ponds were too land intensive, labor intensive and with the
moderate climate of Maryland we could only grow fish for 1/2 of the
By the mid 1980's there were a handful of people around
the world who were beginning to experiment with growing
fish indoors in tanks. The founder of Global Aquatics was
Like everyone else at the time, we started out with a lot of
different tank shapes and designs. Some were large, easy
to build round tanks, other were fabricated rectangular
tanks of various sizes. The theory being that pretty much all
we had to do was to fill the tanks with water, add some fish
and "viola", we would grow the fish... And then the trouble
began. It seems that fish poop in the water and it does not
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We didn't just wake up one morning with a bright idea....
We spent 40 years developing brilliant innovations
WHAT WE LEARNED IN OUR FIRST TEN YEARS
One of the first things a fish tank designer must understand is the dilution factor in a fish growing tank. Unfortunately, many
do not understand this problem and the results is a fish tank that can not sustain very many fish per gallon of water.
The dilution factor simply means, in a recirculating tank full of water, when new water comes in, a certain amount of this
clean water is going to mix with the water that is already in the tank. If the purpose of this new water is to flush out the dirty
water and the mixing of the two is too great, then the tank will never clean itself properly. The results, in a fish tank, will be
that a lot of the fish waste will not leave the tank but will decay and dissolve right there and pollute the water even more.
A vessel holding water is called a tank. However, just because a vessel holds water does not necessarily make it a good fish
rearing habitat nor does it necessarily make it efficient for the operator to manage. Of all the aspects of modern aquaculture
that researchers have studied, none has been more over looked than the size and configuration of the very vessel that the
growing product has to call home until it is ready for market. We at Global Aquatics have never understood why people pay
so little attention to this important part of a system design, especially since we have spent so much time developing what we
consider to be the perfect design when efficiency and management are considered.
Small verses Large:
The key to successful operation of any fish system is "Total Control." This means control over each and every animal in the
tank and control over each and every gallon of water within that tank. Ask yourself these two questions; Why is it that even
under the best of conditions a five acre catfish pond can only produce one pound of fish per 400 gallons of water, while
even a poorly designed tank system can produce 1/2 pound of fish per 1 gallon of water? Why is it that when there is a total
harvest of fish from a pond there is such a wide variation in the sizes of the animals even though they are all the same age
and were placed in the pond at the same time? The answer to both of these questions is "Control", or in the case of the
pond, "Lack" of total control. Now, one more question. What s the difference between a one acre pond and a 20,000 gallon
tank? The answer is, "Some, but not much" What is the difference between a 20,000 gal fish tank and one that holds only
3,000 gallons? The difference is the same as night and day.
It is very important to remember that as a fish farmer you must manage two things at the same time, water quality and the
fish. Obviously the less water you have right in front of you in a vessel, the easier it is to manage. There will be more positive
water exchange from the inflow and less dilution. Thereby allowing for better water quality.
It also goes without saying that the more accessible the animals are to you the easier they are to manage as well. By
managing the animals we are referring to the need to constantly sort the larger faster growing ones from the population at
certain intervals during the growth process. This means that every so often the entire population of the tank must be
separated into other tanks based on the size of the individual animals. The reason for needing to do this is because as in all
animal populations a pecking order occurs whereby the larger, more aggressive animals dominate the rest of the group.
When these dominate animals are removed from the tank and placed with others their same size, a new pecking order will
develop within the remaining population. It is because grading a pond is not possible that there is such a variation in growth
sizes at harvest time. When grading a tank the faster it is accomplished the less stress is placed on the fish. When you have
a large tank containing 25,000 or more animals it may not even be possible to grade this group and if it is attempted it will
likely place some of this group under stress for as much as seven times the amount time it would take to grade the group in
the smaller tank. Grading the fish is also a requirement for harvesting. Generally in an intensive system the fish are harvested
on a continuous basis as they become market ready. Since we know that some of the fish will grow much faster than the
others, it is necessary to be able to capture just the ones that are market size from a huge tank of ungraded animals without
injuring the smaller that still need more growth time.
ROUND VS. RECTANGULAR
It must be remembered why anyone uses round tanks in the first place. A round tank is really just a cylinder holding the
water. Because water exerts pressure equally in all directions when placed in a cylinder, round water vessels can be
constructed very cheaply using the minimum thickness of materials. The advantages of this fact is, round tanks can be
transported to a site and quickly set up. However, this convenience is the only quality of a round tank and this lends no
particular advantage where production is concerned. It should be remembered that it is production that pays the bills and
the fact that the tanks were easy to install should not be allowed to over shadow future performance. The most obvious first
drawback to a round tank is they are space intensive. A round tank in a rectangular room means there is going to be a lot of
wasted space in that room in the corners that the tank does not cover. Another draw back is the fact that a round tank has
no difference in length or width, therefore water circulation can only occur in a circular motion. Many early designers use to
explain that this circular motion was the most effective way to remove solids, because the vortex in the center acted like the
vortex in a toilet. They obviously flunked out of physics class because the two vortexes are caused by different dynamic
effects. In a toilet the vortex is caused by gravity. This occurs when the valve is flushed there is a sudden opening at the
bottom of the bowl. As the water drops through the hole, gravity and the Earth's rotation takes control and causes the water
to swirl around the void left by the water that has already escaped through the bottom. This causes a partial vacuum at that
point and sucks everything into it. In a round tank the circular motion may resemble a toilet vortex, but instead of being
caused by gravity and a partial vacuum, it is being caused by water flow from a pump. This water flow is greater on the outer
edge of the tank then in the center, therefore a certain amount of the solid waste in the tank will travel towards the center.
However, the problem is, waste deposited along the outer edge of the tank may have to orbit the tank hundreds of times
before it finally makes its way to the center. In the mean time it is being churned and homogenized the entire time and can
cause water quality problems as it slowly dissolves. In a rectangular tank the water flow is generally in a straight line from
one end to the other. This would mean that a solid deposited in one end of a 25 foot long tank can only travel 25 feet, and in
one direction, before it hits the bottom solids trap. In most system designs the time required for the trip may only be a matter
of minutes. Therefore the solid is removed in it's entirety before it has a chance to dissolve in the water column and cause
water quality problems.
WHAT WE DID WITH OUR EXPERIENCE
While experimenting with one tank design after another we were also working with different methods to place the clean
water in the tank, the best way to add the oxygen, and design better filters.
One thing we had at the time was a tool no one else in the industry even knew about then. In the late 1950's the founders
father had invented a low head oxygen injector to be used in waste water systems. After some modifications to suit our
purposes we were able to use this devise to precisely direct the incoming water into the tank and at the same time add the
dissolved oxygen the fish needed. Through the use of this injector we cut the dilution rate down to a minimum and kept the
incoming end of the tank filled with clean water while it pushed the dirty water ahead of it and out of the tank to the filters.
While this seems simple enough, we ran into one more problem. When used in a tank that was too big, either in length or
width, or both, some parts of the tank would build up a turbulence and the water would not move, it just sat there.
Unfortunately this happens all too often in most fish tank designs and is difficult to overcome unless things are balanced.
After about another year of experimenting with different tank shapes and dimensions we finally figured it out. The maximum
tank could be no longer than 24 feet in length, no more than 6 feet wide and 4 feet deep. With the injector working at 12psi
and 12 gallons per minute an oscillation is established in the tank that sends the water current flowing back and forth
through the tank, from side to side much like a pool ball bounces from rail to rail to get to the other end of the table. This
oscillation not only moves the water in a positive manner carrying the waste with it, it sets up numerous vortexes that force
the solid waste to the specially designed bottom and out of the fish water column.
With this discovery we now had a true machine.
We had a tank with a fine turned water and
oxygen injection system.
S-09 FILTRATION SYSTEM
During this period of time we also experimented with every type of solids filter we could either find on the market or dream
up ourselves. From sand filters to floating bead filters to various plate filters and clarifier's, we found each had their short
comings. It was the same with the bio-filtration used to removed ammonia and nitrites. We tried everything from shot gun
wads, to hair curlers to small pebbles. Everything had severe limitations.
Recently there has been a lot of news about how the introduction and use of certain Micro-organisms can be helpful in an
intensive aquaculture system. We at Global Aquatics are scratching our heads wondering why all of these researchers are
claiming to have suddenly "Discovered" this amazing fact. You will find most of the of the discussions about this in some of
the aquaponics sites found on the web. We developed this process at our R&D facility in the early 1990's and refined it as
far as we could take it. Our natural aquaponic clarifiers proved to be a great best way to not only remove suspended solids
from the culture water, but also aid in the de-nitrification process to remove ammonia and nitrates through the natural
accumulation of micro-organisms. This system was as close to following the natural process of water purification that one
can get. As a result almost all of the water in a recirculation system could be used over and over again with just marginal
replacement required from the daily flushing of the system to remove trapped solids. For our design we primarily used water
hyacinths as the filtration plants. These are aquatic plants that can take out a lot of nutrient and their roots attract and collect
solids. We chose this type of filtration to use in the S-92 system because this new system was big. Producing 200,000
pounds of fish a year meant we were going to filter out almost 400,000 pounds of solid waste each year.
The final part we needed to complete this system was a bio-filter that could handle the hundreds of pounds of feed we used
every day and the resulting ammonia load from the fish waste.
This system was extremely efficient since it worked entirely on
gravity and used no pumping and no mechanical filters of any
kind. Daily flushing of the system was no more effort that the
removal of a stopper from a bath tub. The solids went to a waste
holding area and then were pumped from there to either the
digester tanks to be coverted into fertilizer for aquaponic crop
production or to other discharge places.
As well as it worked, there were shortcomings for this type of
filter. One was, it was massive, took up a lot of room and was
expensive to build. The second was, the plants that worked best
in here, Water Hyacinths, had no human food value.
Our researchers started looking to other, more compact ways to
filter the water for future systems. (See drum and plate filters)
After experimenting with several different types of media
we settled on a core type of media that would allow water
to be pushed up through it, much like the water in a car
radiator. The walls of the cores would allow for a lot of
area for the bacteria to colonize.
We had learned early on in experiments that when water
from a fish system is allowed to just trickle down through
bio filter media, in time, there would be a build up of
minute particulate from microscopic fish waste and
sooner or later the filter would clog and fail. Being
trapped at the top of the filter it would be very difficult to
clean because the washing away of this material down
through the cores also ment we would be washing away
the bacteria we needed and it would be restarting the
filter from scratch.
After some trials and errors in the engineering of a vessel
that could hold the pressures, we developed the
"Upwhelling" bio filter. With this unit the water was
pumped into the bottom of the tower and up through the
cores. Any particulate would be trapped in the bottom
which could be flushed out simply from the head
pressure of the water column.
This type of bio filter was use very effectively in the S-92
for over ten years. In order to get enough filtration for
200,000 pounds of fish per year we had to use three of
these towers hooked up in tandem.
In the picture above you can see the upwhelling bio-filter and in the background the are aquaponic clarifiers. The dirty
water left the fish tank and flowed first through the clarifiers to remove the solids and then was pumped up through the
bio-filters. When the water left the bio-filters it was allowed to fall the 10 feet to a tank at the bottom. This splash removed
all of the dissolved gases like CO2. Later models included a foam fractionator to remove even the smallest bits of solid
matter before the water returned to the fish tank.