Aquaponics 101 Part Two: System Design

[Oliver]

This is the second in a series of posts that are going to teach you most of what you need to know about Aquaponics. 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.

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).

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 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 Aquaponics system type and its design, but I'll also be referring to other designs. As mentioned in Part One, 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.

As I also mentioned in Part One, 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 Aquaponics farmers (I'm talking about home and backyard farmers here) choose to combine their grow beds and their bio-filters into a single unit. This simplifies the design and construction of their Aquaponics 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 a 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 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 they 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). 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.

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 clean out any plant roots between planting 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 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).

The best way to drain your grow bed is with a Bell Syphon. 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 syphon". At that point, the syphon 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 Syphons here. This information can be found elsewhere on the web, as there are several different designs available. The syphons must be sized properly in order to remove the water from the grow bed in a fraction of the fill time and still function properly. Grow beds using a Bell Syphon 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.

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 Aquaponics 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 use a smaller pump requiring less electrical power as long as other pump sizing requirements are met (more on this in a later post).

Within the Aquaponics 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 Aquaponics 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.

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 50% or decreasing the planned fish poundage by about one third. Some combination of these two adjustments might make more sense.

Many Aquaponics 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 Aquaponics farmer. Some live close to the edge and seem to get away with it, others are not so lucky.

In Part Three I will continue talking about System Design.

[keith_r]

i'm interested in these threads, but do you have data to support statements like flood and drain is better than cf?

i'd like to see data that would support your point of view,,not trying to cause trouble or anything, but i've seen "advise" posted with nothing to back it up.. and i've seen other systems that are in conflict with your statments..

regarding gb depth, how did you arrive at that number?

are you selling ap products/services? (sorry, but i've been "invited" to several presentations about ap, and while they may have some good info, they have no data to backup statements!)

[Oliver]

"i'm interested in these threads, but do you have data to support statements like flood and drain is better than cf?"

Good question. As far as data, most of the evidence is anecdotal and simple logic. 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. Part of what I had edited out due to trying to keep it short was that we used to only flood and drain half of our grow beds. That was when our DO was low. Now we flood and drain all of them; and, along with the other changes, we have much better DO. It is just simple physics and common 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.

"i'd like to see data that would support your point of view,,not trying to cause trouble or anything, but i've seen "advise" posted with nothing to back it up.. and i've seen other systems that are in conflict with your statements.."

I would be interested in the specific conflicting information and the data to support it as well.

"regarding gb depth, how did you arrive at that number?"

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 published surface area of the particular media with which you are working. I didn't go into the numbers here, again, for brevity. Also, as I stated earlier, I have built systems using these numbers and they work well.

One big argument 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. 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, as I will talk about in a future post. After almost two years and twice in that time having to clean out the grow beds full of plants roots, I have found the solid fish waste problem not to exist. This, I believe, is due to the depth of the grow beds allowing time for the solids to break down. By digging into the grow beds while they are flooded, you do find solids in the water in the process of breaking down, but not accumulating in the bottom.

"are you selling ap products/services? (sorry, but i've been "invited" to several presentations about ap, and while they may have some good info, they have no data to backup statements!)"

Not here.

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 price of DO meters.

Oliver

[keith_r]

i appreciate your reply Oliver..
i'm a member of several forums (aquaponics, ponds etc) and try to learn as i go.. i was at a presentation for a guy selling systems, everything was galvanized, fish tanks, gb's.. and when i questioned him about it he stated that he'd been doing it that way for years with no issues.. on another forum i follow someone experienced some fish deaths, and had galv tanks (not lined), after this happened to a couple people someone got the smart idea to have their water tested and found toxic levels of metals that had leached from the tanks..

on the byap forum they are trialing 3 growbeds side by side from one ft, one is cf, one is flood and drain and one is timed flood and drain, the cf bed has been showing better performance of all but a couple of plants, it's easier to follow a recommendation when there is visual proof..

your point about DO levels has been demonstrated on many forums.. gb depth though, i've seen great performance out of "shallow" beds and planting things that don't need the depth, but personally i think deeper would be better, there's a system of one of the members here (TCLynx) that is using rubbermaid totes for gb's 20" deep, these aren't being "completely" drained because she drains out the side, again she shows tremendous results..

i take pretty much everything i read with a grain of salt, but with a well documented system (pictures/dates etc), including failures/issues etc beats the hell out of a verbal argument every time

i'd be interested to know how you arrive at that stocking density as well...

[urbanfarmer]

i appreciate your reply Oliver..
i'm a member of several forums (aquaponics, ponds etc) and try to learn as i go.. i was at a presentation for a guy selling systems, everything was galvanized, fish tanks, gb's.. and when i questioned him about it he stated that he'd been doing it that way for years with no issues.. on another forum i follow someone experienced some fish deaths, and had galv tanks (not lined), after this happened to a couple people someone got the smart idea to have their water tested and found toxic levels of metals that had leached from the tanks..

on the byap forum they are trialing 3 growbeds side by side from one ft, one is cf, one is flood and drain and one is timed flood and drain, the cf bed has been showing better performance of all but a couple of plants, it's easier to follow a recommendation when there is visual proof..

your point about DO levels has been demonstrated on many forums.. gb depth though, i've seen great performance out of "shallow" beds and planting things that don't need the depth, but personally i think deeper would be better, there's a system of one of the members here (TCLynx) that is using rubbermaid totes for gb's 20" deep, these aren't being "completely" drained because she drains out the side, again she shows tremendous results..

i take pretty much everything i read with a grain of salt, but with a well documented system (pictures/dates etc), including failures/issues etc beats the hell out of a verbal argument every time

i'd be interested to know how you arrive at that stocking density as well...

I don't think there's a "one size fits all" type AP system. There are SO many variables you can't just say what works best for someone in California is going to work for someone in Florida. The type of plant, climate, and many other conditions can affect exact performance. I'm not saying anyone is right or wrong, but rather what you find what works best for you, well... works best for you!

On the depths of the grow beds, I just learned today that the commonly held belief that a tree's root system mirrors the branches above is NOT true for Florida planted trees. They tend to spread out far and not deep, often times 3 times the length of the branches. This is because the roots simply don't have deeper soil to grow into... similar to shallow grow beds. Sure, we can discuss the microbes and so on and so forth, but I just want to point out that with evolved multicellular life forms, they tend to have advanced mechanisms for survival. If anything, it is a bit arrogant to believe we know best given our tiny amount of knowledge for all circumstances when there are more variables than there are facts or answers. Trail and error is the way to go while using what we do know as a GUIDE and NOT GOSPEL. Plus if it doesn't work out, you can rack up kills to become a REAL fish farmer, right?

[Oliver]

keith_r

In writing this I knew that these kinds of questions and challenges were going to come up. That is why I took care in my wording and am saying that this is not cast in stone. I have to look at my post for in my mind I am several posts ahead of what is published. I find it gets a little confusing for me to keep track of what you have read.

The stocking densities are like everything else, a combination of others and my own experience. As our fish grew out, I watched carefully the system chemistry. As we planted different plants and watched them grow and some flower, I noticed the chemistry change. Later, as the fish got bigger and we fed them more food and a second planting happened, I noticed the chemistry changing as it did with the first planting. I also noticed that it was becoming more difficult to keep the system in the acceptable range and balanced. That was when I focused on increasing the DO in the water. Over time and a number of changes to the system it has come back into balance and stayed there. I keep a log of every change in the system and record all the numbers in it. This includes the usual water chemistry as well as the amount of food given the fish (automatic fish feeders with precise metering of food), tank temperatures, DO in each tank. pH, and TDS, as well as any fish death or tank change.

Once the fish reached one pound per three gallons of fish tank water, I again noticed a sensitivity in the balance. More DO was added and it again settled back down. At this point there is not much, short of adding pure oxygen to the water, that I can do to keep the system stable if I increase the poundage of fish; for the DO is currently between 6 and 7 ppm. So, I have concluded, as have others, that the one pound per three gallons of water, given the volume of grow beds I currently have in the system, is a maximum. This is where I came up with the number of 3.3 pounds of fish per gallon of grow bed capacity. The reason for the 3.3 pounds is because we only have five grow beds (due to space limitations) when ideally we should have six, so I have calculated the ratio to show our actual grow bed to fish density ratio. If I increase the number of grow beds (which will require a redesign of the system) then it should be possible to up the number of fish. But this will compromise the idea behind this series of posts, which is to tell how to build a simple Aquaponics system that will produce food without pushing the limits of Aquaponics design. I want people who are new to Aquaponics and are building and operating their first system to be successful.

By the way, we have some fry and fingerlings in one of our three connected (water exchange only, no fish exchange) tanks. As they grow out I will be keeping an eye on the chemistry as always and it will again challenge they system. It may be time then to harvest some fish, as we have yet to do that.

Oliver

[Oliver]

urbanfarmer

"I don't think there's a "one size fits all" type AP system. There are SO many variables you can't just say what works best for someone in California is going to work for someone in Florida."

As long as the environment is the same (and it usually isn't) then the science will work the same. I agree that not everything can be distilled down to pounds, gallons and ratios. But, we do the best we can to understand what the process is and what is going on in any Aquaponics system and then apply what we learned in the next system, regardless of location. Even two identical systems in the same location will respond differently; which is only to say that regardless of what we may think, they really aren't identical after all.

"If anything, it is a bit arrogant to believe we know best given our tiny amount of knowledge for all circumstances when there are more variables than there are facts or answers. Trail and error is the way to go while using what we do know as a GUIDE and NOT GOSPEL. Plus if it doesn't work out, you can rack up kills to become a REAL fish farmer, right?"

The Aquaponics experience tends to weed out arrogance once some of your fish die. And, yes, this is just a guide; but my hope is that I have landed somewhere near the center of the bell curve when it comes to the advise I am giving here. Obviously, I am taking some risk in putting this information out on a forum; for I know that not all will agree with these suggestions. But, that is why I asked JCO to unlock this area so we could have a good and lively debate.

Oliver

[urbanfarmer]

I think you're doing a great job Oliver! Very few people put in the time and dedication to help others. Keep up the hard work.

[stucco]

I think you're doing a great job Oliver! Very few people put in the time and dedication to help others. Keep up the hard work.

+1

[rfeiller]

+ another.

used as a starting point guide for those of us without the experience will at least minimize the failures and maximize the possibilty of success. we can adapt any variations from there as deemed needed.

a little success goes a long way to help keep new folks in the aquaponics program and insure further successes.

i appreciate the unselfish manor in which the members are willing to help each other to have success.

rich