Aquaponics 101 Part 2: The System Design
This is the second in a series of Tutorials on Aquaponics 101 that are going to teach you most of what you need to know about Aquaponics (AP). So, if you're curious about the most amazing food growing technology on the planet today, keep reading and scrolling.
In Part 1, "The Bio-Chemical Process", I talked about what Aquaponics is and why it is important to Preppers (those preparing for what is about to come down the pike).
To quickly review, Aquaponics combines the raising of fish and using the fish waste as plant nutrients so you can grow vegetables. This is done year-round and can provide food fish and veggies for your family.
The bio-chemical process includes the breakdown of fish waste into plant nutrients, the uptake of these nutrients by the plants being grown in separate grow beds and the cleaning of the water to be returned to the fish tank and reused in an endless loop. This is all done in a continuous flow recirculating aquaculture system called Aquaponics.
I'm now going to focus on a particular AP system type and its design, but I'll also be referring to other designs. As mentioned in Part 1, the fish tank and grow beds are separate entities. This precludes growing the majority of your vegetables directly in the fish tank. However, some green leafy plants like lettuce can be grown on rafts floating in the fish tank as long as the particular fish being raised don't eat the plant roots. However, this is generally not done and tilapia love plant roots.
As I also mentioned in Part 1, there is a need for a bio-filter, which is a part of the system; and it is filled with a media that contains lots of surface area on which the bacteria live. Most AP farmers (I'm talking about home and school farmers here) choose to combine their grow beds and their bio-filters into a single unit. This simplifies the design and construction of their AP system in addition to saving cost and space. It is this combined system I will be focusing on here.
The combined grow bed/bio-filter containers (from here on referred to as grow beds) need to have enough volume to contain ample material with enough surface area to support the number of fish (by total weight) in the fish tank. They also must provide enough planting area to support the optimum amount of plants needed to uptake the nutrients without depleting the system of these nutrients, thereby causing poor plant growth. Seems complicated; but, fortunately, many have gone before us and have worked this all out. We can build on their shoulders.
Grow beds are generally filled with media, either expanded clay or smooth river stones (gravel), in order to give the needed surface area on which the bacteria thrive, while simultaneously holding the plants in place. The grow bed is filled with the media to a level near the top of the grow bed container, and the fish tank water is pumped into the grow bed filling it to a maximum level that is one inch below the top of the grow bed media. This one inch barrier is to prevent the top of the grow bed media from becoming and staying wet, thereby preventing algae growth on the top of the media. This barrier also helps prevent the bottom leaves of plants in the grow bed from becoming wet and moldy.
The optimum grow bed container depth is about twelve inches. This will allow for at least eleven inches of media and ten inches of fish tank water to be placed in it, which is enough to provide for bacteria growth as well as providing ample depth for anything you wish to grow. It will also allow for some accumulation of fish solids in the bottom of the grow bed and give them time to break down before they over accumulate. Grow bed containers deeper than 12 inches are more costly to fill with media, heavier and transfer more water back to the fish tank (more on this later). Generally, deeper beds are unnecessary, unless you're using gravel as a grow bed media. Then, the extra depth can be beneficial (more on this later, also). Grow bed containers less than twelve inches deep cause your planting area to grow bed volume ratio to be less than ideal, thus creating more planting area than the bio-filter volume can support (depending on what type of plants you have in the grow bed) and an accumulation of fish waste in the shallow beds. This twelve inch number is not cast in stone; but if you build a system using it, it will work. If you use other depths, especially less, then you are on your own. This is the basic design of all our we build and sell.
The size of the grow bed can be whatever you wish; but understand that if you go over 30 inches in width, you will have difficulty reaching across it. For wider grow beds you will need to have plenty of walk around room to get to two opposite sides. Forty eight inches is probably the maximum width you should be considering. The length is not as important as the depth and width. It is best to have at least two grow beds in your system rather than just one. This will allow you to shut down one bed to clean out any plant roots between plantings while still having your other grow bed working to keep the water clean and safe for the fish.
There are two different configurations of media-filled grow beds, flood and drain (also called ebb and flow) and continuously flooded. Flood and drain are the best, regardless of the types of plants you are planting, because it provides the best distribution of incoming nutrient rich water throughout the bed as well as adding aeration to the wetted media and plant roots where the bacteria live. This also adds dissolved oxygen (DO) to the water being flooded back into the bed and then returned to the fish tanks.
You will need a way to flow the water into the grow bed. The water entry point into the grow bed depends, in part, on the shape of your grow bed and how you plan on using it. With a flood and drain grow bed, the point of entry of your water is not critical; but it should have an unrestricted opening so as not to clog with fish waste solids. Do not attempt to spray your water into the grow bed, for the spray holes will clog up in short order (experience speaking here).
This is our favorite Media. It's called Hydroton. It's made from an expanded clay material that is pH neutral. (We'll talk more about pH later in this tutorial).
Hydroton is easy to work with because it's buoyant and pH neutral. When you need to get roots out of your siphon, this becomes a real advantage. So is the fact that it has lots of surface area.
One of the best ways to drain your grow bed is with a Bell Siphon. This is a device with no moving parts that, when the grow bed is filled with water, starts to syphon out all of the water in the grow bed down to a preset level before "breaking siphon". At that point, the siphon action stops; and the grow bed starts to refill. The design of this syphon is critical in order to get it to do its job in a timely manner. I'm not going into the design and construction of Bell Siphons here. This information can be found elsewhere on the web, as there are several different designs available. The siphons must be sized properly in order to remove the water from the grow bed in a fraction of the fill time it takes to fill the bed and still function properly. Grow beds using a Bell Siphon have water continuously being flooded into them at a slower rate than the syphon drains the water out, so you get a flood and drain cycling action. It is important to have a continuous vertical drop (down hill all the way) of at least 6 inches (the more the better) below the siphon so the water is drawn out of the grow bed.
The more often you flood and drain your grow beds, the more dissolved oxygen will be added to the water returning to your fish tank. You should count on cycling your grow beds at least four times per hour. Not only does the design of the syphon influence the cycle timing, the rate at which you flow water into your grow bed, does as well. This cycle timing is one of the most critical parts of the design of an AP system. Needless to say, you will need enough pumping power to exchange most of the water in your grow beds four times an hour.
Keep in mind that once the grow bed media is in the grow bed, it will displace at least 50% (expanded clay) of the volume of the grow bed (more for gravel) leaving half or less of the original grow bed volume for water. This should be taken into account when sizing your water pump. The good news is, you may be able to use a smaller pump requiring less electrical power as long as other pump sizing requirements are met (more on this in a later part).
Within the AP community, you will find differing opinions on the numbers I'm about to give you; but I believe them to be the most accurate based upon what I have learned from those with years of experience in building and testing different combinations of system sizes and ratios, as well as from my own experience in verifying these numbers. You can build an AP system any size you desire, for it is the ratios of the various component sizes that really mater. So, lets start with the ratio of the fish tank size in gallons to the grow bed container size in gallons. There should be about a one to one ratio between the fish tank and grow bed container size. This is assuming that you are using media filled grow beds.
Here is a great Bell Siphon that I designed and built for our Food Forever™ Growing Systems; and it works like a charm.
One of the best features it offers is it's wide mouth, which is 4" in diameter. This wide mouth allows you to reach right into the siphon and clean out any roots that may have taken up residence. It is also easy to insert and remove the Stand Pipe.
Media filled grow beds are ones that use a growing media such as expanded clay or gravel to fill the beds. It has been found that the amount of grow bed volume needed to support a system is more related to the pounds of fish in the tanks and how much they are fed than the amount of water in the system. If you are using expanded clay as a grow bed media, a good rule of thumb for the size of grow beds is 6 gallons of grow bed (minimum) container size for every pound of fish you plan to have in your system at maximum fish grow-out size. If you plan on a ratio of six gallons of water per pound of fish in the fish tank, then this works out to about one gallon of fish tank capacity to one gallon of grow bed container capacity when using expanded clay as a grow bed media.
For gravel media in your grow beds, you should consider increasing the size (depth) of your grow beds by about 30% or decreasing the planned fish poundage by about one third. Some combination of these two adjustments might make more sense.
Many AP farmers are pushing these numbers in their systems and will argue for what they are doing. I am trying to give you what I believe are optimum parameters here for a system that will have the highest probability of working and allow you the greatest possibility of success as a first time AP farmer. Some live close to the edge and seem to get away with it, others are not so lucky.
As to the difference between flood and drain grow beds and continuous flow grow beds, it is well known that some plants won't grow well or at all in constant flow grow beds; for their roots need more oxygen than do other plants. Flood and drain supplies this needed oxygen while constant flow does not. Logically then, the bacteria living in the grow beds would do much better with more oxygen. We used to only flood and drain for half of our grow beds and did continuous flow for the rest. That was when our DO (dissolved oxygen) in the water was low. Now we flood and drain all of our media filled grow beds; and, along with the other changes, we have much better DO. It is just simple physics and logic that the water flowing through a constant flow grow bed is not going to get as good of an even distribution of nutrients and oxygen as a flood and drain grow bed, which does a nearly complete grow bed purge with each cycle.
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Or get a piece of paper & a pen and take the Part 2 Knowledge Quiz below:
(showing One Grow Bed)
Shown here is a Dissolved Oxygen meter. Go to our for everything you'll need to know about this handy (and from my perspective) much needed DO measuring device.
DO Meters take the guesswork out of determining what's going on in that very important part of the Bio-Chemical Process; and well oxygenated fish are happy fish.
As to the grow bed depth, it is a number that has been tested by those who have been working with flood and drain aquaponics grow beds for many years. It has to do with the surface area of the particular media with which you are working.
One big debate is the removal of fish waste solids. Those who use deep (12" or more) grow beds generally find that they do not have a problem with over accumulation of these solids for a considerable amount of time. Those with shallower grow beds tend to complain about the accumulation of fish waste solids. I hedge my bets on this by weekly adding heterotrophic bacteria, and I will write about this product in a later part.
After several years of running deep media grow beds, and yearly cleaning out just plant roots, I have found the solid fish waste problem not to be a big one. Around our fifth year, we ran into some undissolved fish waste solids when planting and decided that completely cleaning the beds, meaning removing the Hydroton, washing it and the bed. Doing this about every year or two would be a good idea. This is a low maintenance recommendation for your deep media beds. I believe the deep media beds only need this minimal maintenance due to the depth of the grow beds allowing time for the solids to break down and the abundance of dissolved oxygen as well as the weekly adding of the Heterotrophic bacteria. If you follow this maintenance advice, when digging into the grow beds while they are flooded, you will find solids in the water in the process of breaking down, but you will not find them accumulating in the bottom.
There is a lot of research available that shows the importance of DO levels needed for both plant and fish growth, and the science of nitrification clearly indicates its necessity. The flood and drain process also has been shown to increase oxygenation of the water in the grow bed, which gets returned to the fish tank. The deeper the grow beds, the more surface area there is for both the nitrification process to take place as well as oxygenation of the wetted surface area of the substrate media in the grow bed. The oxygen only goes a few molecules deep into the water surface, so the more surface area, the more oxygen is dissolved and eventually returned to the fish tank.
I need to impress the importance of high levels of DO in the system, for it is the prime ingredient that is required in every aspect of the process. Anything that one can do in the system design and operation to increase the DO will benefit the whole system. Unfortunately, this is usually mostly ignored, I believe, because of the cost of DO meters.
"I'm so pleased you decided to continue with your Aquaponics 101 tutorials. After each Part, there will be a Quiz Board so you can test your knowledge.
If you missed the Quiz Board, you can go back to Part 1. If you're ready to move on, just start by reading and studying the information below.
Part 2 is all about
System Design." OLIVER