Post by: AquaponicsUSA
This is the third in a series of posts that are going to teach you most of what you need to know about Aquaponics. These posts are part of a book we are writing and will be selling on our website. So, if you’re curious about the most amazing food growing technology on the planet today, watch for this series of educational posts on Aquaponics and please, become interactive by making comments or asking questions. Given the state of our Union, the motto on our website is becoming more important than ever–“Time To Grow Food”.
In Part One, “The Process”, I wrote about what Aquaponics is and why it is important to Preppers (those preparing for what is about to come down the pike), the fact that you can grow food for you and your family year round as long as your Aquaponics system is in the proper environment. I also gave a description of the biological processes involved that make Aquaponics work.
In Part Two, “The System”, I wrote about the components of a basic system.
To quickly review, I wrote about the need for a bio-filter and that it is usually combined with the grow bed to form a single Aquaponics component called the grow bed, which is the most important part of an Aquaponics system. I told you about the grow bed media, the grow bed shape, and that you need about one gallon of grow bed/bio filter volume for every gallon of fish tank volume and the reason for this ratio.
So, let’s continue with the discussion on system components.
Some will argue that the standard is two gallons of grow bed container capacity to one gallon of fish tank capacity instead of the one to one ratio I mentioned in Part Two. Again, the number for Hydroton is 1:1 and for gravel about 1.5:1 gallons of grow bed container capacity to fish tank capacity. You can use the 2:1 number only if you flood and drain some of your grow beds but not all; or if you add a sump tank to catch the water that would otherwise be returned directly to your fish tank.
The reason for this one to one ratio limitation is that the simplest Aquaponics design has a low to the ground fish tank that is 24 to 30 inches high and grow beds that are up on tables high enough so that the water pumped up from the fish tank to the grow beds can gravity flow back into the fish tank from the bottom of the grow bed syphon. I prefer 24 inch high fish tanks so the grow beds don’t need to be so high and, therefore, you don’t need a step up to comfortably reach across them. This allows for at least six inches of extra syphon draw down below the grow bed thereby reducing the grow bed’s drain time (more on this later).
The grow beds’ syphons activate on their own timeline; but at some point, with multiple grow beds, the syphons arrive at nearly the same schedule. Like two or more metronomes, occasionally they all sync up and drain at the same time filling the fish tank to capacity and then simultaneously be pumping water into and filling all the grow beds. With a two to one grow bed to fish tank ratio, the extra water required to fill the grow beds leaves the fish tank with a dangerously low amount of water, which will stress the fish. With a one to one grow bed to fish tank volume ratio, the water level in the fish tank won’t go so low as to stress the fish. So, one to one is the number you want to aim at in your Aquaponics system design.
Some will argue that one way to avoid this water level in the fish tank problem created by increasing grow bed volume is to add a sump tank (mentioned above) that catches the drained water from the grow beds. Then that water is pumped back to the fish tank from the sump tank after it’s water reaches a certain level by way of activating a float switch connected to a submersible pump in the sump tank. This allows the sump tank to absorb the intermittent water flowing into it and helps keep the fish tank from experiencing major swings in water level during grow bed syphoning.
For a short fish tank that sits on the ground, this requires an extra pump (in addition to the one in the fish tank) and a float valve switch (mentioned above) in the sump tank, which adds extra parts, cost and potential points of failure. Turning a pump motor on and off repeatedly shortens its life, and, if either the pump motor or float valve switch were to fail (and eventually one or the other will fail), you will have water all over the place, a fish tank void of water and dead fish. In my opinion, this is not a good design.
Other system designs raise the fish tank or have a tall fish tank, like a tall IBC tank with its top cut off, that overflows through a pipe into grow beds that are positioned at a lower level. The water returns to a low siting sump tank from the grow bed syphons and directly from the fish tank overflow where a continuously running submersible pump is pumping water from the sump tank into the fish tank. Additional plumbing is used to be able to divert the water as needed for system maintenance without turning off the complete system and to adjust the flow of water into the grow beds. It is an elegant design because it adds only minor complexity and cost to building your system while using a single continuously running pump, and it works well. It is very important that a float valve be added that feeds extra water into the fish tank in order to keep the water level nearly constant; for evaporation from the system will reduce the water level in the fish tank to a level where it won’t overflow, thereby starving the pump in the sump tank.
The simplest of systems has a submersible pump in a low fish tank that pumps ample water under pressure to the grow beds. The water can be controlled by valves at the grow beds in order to regulate their fill rate while providing some additional water under pressure to be jetted back into the fish tank for added aeration. This extra pump pressure allows for purging of the lines to the grow beds by fully opening the grow bed control valves individually for a short period of time. This needs to be done periodically because the fish waste solids are heavier than water and the slow flow up to the grow beds doesn’t allow for all of the solids to make it into them. This slow upward flow causes some accumulation of solids in the plumbing, which the purging alleviates.
The auto syphons return the water to the fish tanks from the grow beds by gravity. This is accomplished by using a line connected from the bottom of the syphons below the grow beds to the fish tank above the water level. The grow beds are high enough without being too high, and the fish tank is low enough to allow for a good flow return from the syphons. This pretty much describes the FOOD FOREVER™ Growing Systems I have designed (minus the aeration), which are elegant in their simplicity and very cost effective. Again, to be clear, I have borrowed significantly from other’s tried and tested work.
Grow beds can be made of wood with plastic liners, but fitting them with the needed bulkhead fittings that don’t leak may prove to be a challenge. However, it is successively done all the time. The bulkhead fittings in the grow bed bottoms are necessary and are part of the syphons. Some Aquaponics system builders use flush valves and slowly filled plastic water bottles instead of syphons to trigger the flush valves. I am told they work quite well and are very adjustable while adding minimal moving parts and complexity even though they are not very aesthetically appealing.
Hydroponics reservoirs make good grow beds (at least the twelve inch deep square black ones do). These seventy gallon, ten plus square foot (one square meter) reservoirs are what I use in most of our systems, and they are very sturdy. These reservoirs do need bottom support when used as elevated grow bed containers because they are made to sit on the floor. The rectangular white ones are very flimsy, somewhat pricey; and I wouldn’t recommend them, even though they have a nice form factor of thirty inches wide. They can be used with some side and bottom support. I am always on the lookout for improved system components and upgrade our systems when they are found. This is an on-going process.
I recommend using animal stock tanks as fish tanks. They are twenty four inches tall and, depending on the brand, are very well made from USDA approved polyethylene with UV inhibitors. You don’t want to have a black fish tank because it limits the light in the tank making it hard to see the fish. Many fish species do better with more light.
As for submersible pumps, I recommend magnetic drive (mag-drive) pumps because the motor is in its own sealed compartment and should never leak any oil out into the fish tank water, which would be really bad for the fish. Good ones are relatively inexpensive and have a three year warranty. The pump should be capable of turning over the total gallons in the fish tank about every thirty minutes at six feet of head pressure minimum. Be careful of advertised flow rates at zero head pressure because that doesn’t tell you what you need to know for your system (more on this below).
In sizing your pump, make sure you have enough flow to fill all of your grow beds at least four times and hour. For example, let’s say you have a 120 gallon fish tank and two 70 gallon hydroponic reservoirs as grow bed containers for a total of 140 gallons of grow bed capacity. The water in the grow bed will only be filled up to the 60 gallon mark, for a total of 120 gallons for two grow beds. The grow bed media will displace half of that so now we are looking at about 60 gallons of water total in the two grow beds. Not all of the water will drain, so let’s say about a total of 50 gallons drains out before syphon break. We replace that four times an hour so we need 4 X 50 = 200 gallons per hour just to fill the grow beds. We need another 20% to jet back into the tank for additional aeration, which is 40 gallons per hour. The total water is 200 + 40 = 240 gallons per hour at 6 feet head pressure. This works out to be twice the fish tank volume every hour.
Pumps come in discrete sizes, so we use a 300 GPH at 6 feet of head pressure pump. The rule is to always over size your pump in case you wish to add other components to your system later that require water under pressure, like vertical grow towers or an elevated small brooding tank, both of which can gravity overflow back into your main fish tank.
You should never have any metal in your system or plumbing, including the fish tank, metal grow bed containers without liners, valves, especially copper, zinc or brass because they will leach toxic metal into the water and kill your fish. Just stay completely away from any metal coming into contact with your system water with the exception of iron or stainless steel.
We use diaphragm type air pumps that require the diaphragms to be replaced after about one year of continuous use, but they are very inexpensive and easily changed. Air pumps are notoriously inefficient. They produce lots of heat and move little air, but they are absolutely essential for your Aquaponics system. You will need a pump rated at about 7.5 GPH of air for each gallon of fish tank capacity. With a change from 5 GPH to 7.5 GHP per gallon of fish tank water (a 50% increase), we saw a better than 1.5 ppm increase in DO (dissolved oxygen).
The best way to put air into the tank is through AquaFuse lines. With the change from air stones, and their associated relative large air bubbles, to the AquaFuse lines, and their smaller bubbles, the dissolved oxygen (DO) went up over a whole point (ppm).
An addition we made to our systems included placing two 4 foot AquaFuse lines underneath the Hydroton in each ten square foot grow bed and pumping 600 GPH of air through them. We are not sure how much DO this adds, but we do include this with each of our systems.
Our DO regularly measures between 6 and 7 ppm depending on water temperature. Before we made the above changes, it was down around 3 to 3.5 ppm. Studies made with tilapia and varying amounts of dissolved oxygen (DO) in the water show a doubling of growth rate from a DO of below 3 ppm to a DO above 6 ppm.
Air pumps need to be run 24/7, to do otherwise is to kill fish. After all, how long would you last without air?
This, and the previous post, describe one type of Aquaponics system with some variation; but, by no means, covers all of them. I’ve also shared a lot of information about the design of the systems we build. Because we buy in quantity, we get wholesale pricing. We cut, glue, drill, combine components and offer these properly designed ready-made systems for what many would pay if they bought the parts retail. For those of you who will be building your own systems, we’re sharing these details about how to build them yourself because we really believe food shortages are coming; and we want to help as many people as possible get prepared. So now you can buy the parts from various vendors and build your own custom systems. As long as you follow the above suggestions, you will have a system that has the potential to work well and produce food because it is properly designed.
Part Four will be about System Start Up.
L. Oliver Duffy
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