Grow

Beds

What is a Grow Bed?

The Aquaponics USA Food-Growing systems have two main components--the Grow Bed and the Fish Tank; so that’s where all the action is taking place. It’s pretty easy to see the action in the fish tank. Just check out our web cam on the “Our Tilapia” page. But seeing the action in the Grow Beds is more difficult. A little time-lapsed photography will do the trick and a real high powered microscope. The time-lapsed photography is easy (we did a 17 Day lapse to get the pictures below). As for the microscope, we’re going to let an advanced Science Class handle that in the future  while we describe in words here what’s going on in the Grow Bed that can’t be seen with the human eye.  

Just like the Fish Tank, the Grow Bed is an ecosystem unto itself. Because it’s filled with Hydroton (see our Products Page “Hydroton” for more details) it acts like a bio-filter breaking down the fish waste as it passes through the Bed. Bio-filters work by growing friendly bacteria on a substrate, like gravel; and here’s where Hydroton is worth it’s weight in

gold. Unlike gravel, Hydroton is porous and, therefore, rich with lots of surface area where these friendly bacteria can hang out and break down the fish wastes into soluble nutrients that can then be available for use by the plants and the aquatic life. 

In a very short while, the company that makes Hydroton, Oekotau Easy Green, will be marketing their newest Grow Bed Media exclusively for Aquaponics which they are calling Aquaponics Grow Bed Media. Aquaponics USA is pleased to announce we will be the first company to use their Aquaponics Grow Bed Media and we will demonstrate how adding a mix of smaller Hydroton pellets to the original composition of Hydroton will offer the Aquaponic farmer even more rich surface area for a superior Bio-filter.

By running the water through the grow bed, these nutrients get taken up by the plants and the water is returned to the fish cleaned and ready for the next cycle. The scientific name for this process is called the Nitrate cycle. Nitrate is what you want to end up with--a high Nitrate count while your Nitrite and Ammonia counts remain very low because they can bring toxicity (even death) to both your plants and your fish. (You can read more about this subject on the “Water” Page). So, the first answer to the question, “What is a Grow Bed”, is: The Grow Bed is a Bio-filter.

The Grow Bed is a Container for your Plants.

The Grow Bed’s more obvious job is to act as a container for your plants. We’re assuming you’re growing vegetables; but all kinds of other plants can be grown in your grow bed like tropical house plants, orchids, etc.  The Aquaponics USA systems utilize water (not soil) as the main nutrient delivery system so the Grow Bed functions to hold the water, the media and the plants.

Some folks building and selling aquaponic systems today seem to be stuck in an arms length marriage of aquaculture and hydroponics, continuing to use the numerous and cumbersome components of both while limiting their vegetable output to green leafy plants like lettuce; for this is all that their systems will grow. While this was the way that modern aquaponics began, much has been learned since then. By reducing the fish densities to the above numbers and balancing the grow bed to fish tank size ratio, many of the components in the earlier system designs can be discarded, like the clarifier mentioned above.

If you are looking to maximize the pounds of fish output and count your vegetable output by the number of heads of lettuce you can grow in an NFT or raft system, then an external bio-filter and clarifier will be needed. However, this type of system can be unstable. The water quality can change rapidly and if you are not on top of the problem and implement a solution quickly, you will lose fish. On the other hand, for a system that remains stable over time with minimum attention, grows a variety of vegetables in an ebb and flow grow bed, use the numbers given above that have been proven to work.

Our Aquaponics USA greenhouse set up has three of our offered systems in current operation in a five grow bed configuration. That means we have installed two FGS-2s and one FGS-1 system in order to produce lots of different veggies. We use the same automated fish feeders we offer on-line as a system add-on. We test our water weekly and add water at that time to replace any that has evaporated during the week. The only water that’s being replaced is the water that evaporates out of the system. The systems are stable and producing with minimal fish loss. With 50 fingerling Tilapia in one of our three tanks, the most dense, we have lost only one fish, and that happened shortly after the shock of transportation. In the weeks since then, the remaining 49 have been healthy, eating well and growing. You can see them on our Live Tilapia Cam on the "Our Tilapia" and “Greenhouse” pages. The plants have taken over the greenhouse as can be seen on our live Web Cam on our "Greenhouse" page.

We offer follow-on support in both the system set and any other questions that will arise in starting up your system. We also support system upgrades, and those we feel are necessary for proper system operation are free, as we have already done so with systems in the field.

We have set up a support phone line just to help those customers who have purchased one of our systems and need a little hand holding. Our contact information can be found on our “Contact” page.

The following are Pictures of the Grow Beds time-lapsed for 17 Days. When you compare these pictures with the Greenhouse Web Cam pictures, you’ll see the growth that’s taken place since the last pictures were taken.

We added an outdoor Sun-Screen Room on the left side of our Greenhouse which explains the turquoise color coming through this picture.

What we have witnessed.

We have seen phenomenal plant growth in relatively short periods of time. Plants grow overnight and that’s not an exaggeration. One mistake we made was to plant too many squash; and they’re hogging Grow Bed space. We’ll be adding a page about plant nutrients, how to plant seedlings, harvesting and replanting soon. So keep your eyes on this site as it’s always in motion.

Here’s a detailed Description of the Relationship between the Grow Beds, the Fish Tank size, the Bacteria, the Fish Food and the Waste in a System Design.

This is a microscopic view in words for those of you who are technically inclined and really like to crunch the numbers, as the following explains these relationships in great detail. Enjoy.

The Aquaponics USA system does not have a separate clarifier like those used in aquaculture (raising fish for food) nor would we want it to have one. It is one of the cumbersome components that has been eliminated in recent years by people making advancements in the technology. The grow bed is the bio-filter. This is where the solid fish waste is collected and becomes fertilizer for the plants. From here on, the term "Grow Bed" is used to refer to the combination grow bed / bio-filter.

This plant fertilization is accomplished by Heterotrophic Bacteria conversion, which describes how specific bacteria convert solid fish waste into ammonia and other elements over time. These bacteria occur naturally in the system. This ammonia, along with the ammonia produced directly by the fish, is converted into nitrites and then nitrates by other bacteria in the system.

Because aquaponics originated as a marriage between aquaculture and hydroponics, there are still many myths about aquaponics, some of which are hold-overs from aquaculture. In aquaculture, the fish waste must be disposed of as the fish to water ratio is very high. It is dealt with by using a clarifying filtration unit that removes the solid waste. The ammonia from the fish in aquaculture is converted to nitrates in a separate bio-filter containing a media with lots of surface area. This ammonia to nitrate conversion is the same process used in aquaponics, except now, the bio-filter is the plant's grow bed; and the plants take up the nitrates. The nitrates are removed in aquaculture by constant water exchange and, therefore, aquaculture is water use intensive.

Because the nitrates are removed in an aquaponics system by the plants in the grow beds, the plants become, along with the bacteria, part of the bio-filter process. The cleaned water is then returned to the fish tank, free of most solid fish waste; and with continuous cycling, the ammonia is converted out of the system. In a fully cycled system, one which has been in operation for several weeks, the ammonia level is very low as the fish are constantly producing it, and the nitrate levels are high enough for the plants to be in a good state of growth. The water is recirculated through this closed system making it the most water conservative food-growing process on the planet today. That’s one of the big advantages to using aquaponics--water conservation in a time when it is of utmost importance.

The fish to water density in an aquaponics system should be kept below 1 pound of fish for every 2 gallons of water. With 6 gallons of water in the system for every square foot of grow bed, the fish waste to plant biomass ratio is adequate for the plants to clean the nitrates from the water through absorption. This works out to 3 pounds of fish for every square foot of grow bed area, assuming a fully grown out grow bed. This is a maximum number and should only be reached in a mature system, one that is at least one year old. A more conservative, and therefore safer ratio, is a “fish to gallon of water” ratio of 1 pound of fish to every 3 to 5 gallons of water in a new system, one that is less than a year old. A move to lower ratios should be done slowly, while watching the water quality along the way.

There are other rules of thumb, such as 1 gallon of fish tank volume for each 1 gallon of grow bed volume. This ratio allows for the solid fish waste to beak down in time without over accumulation. It is better to have a higher grow bed to fish tank volume ratio than it is to have too little grow bed to fish tank capacity. This is usually accomplished by using deep grow beds, those about 12 inches deep. However, grow beds of around 9 inches deep can be used if the other ratio requirements are maintained. Any grow bed depth less than 9 inches becomes problematic, for it is difficult to maintain the other required ratios when designing a system.

It is good to remember in grow bed design that the grow bed container depth is what is referred to and the grow bed media is usually one inch below the top of the grow bed container. The maximum water level should be one inch below the top of the grow bed media at its highest due to the need to keep the bottom of the plants dry and to keep the sunlight off the water in order to prevent algae growth. This leaves only 10 inches of bio-filter in a 12 inch deep grow bed and 7 inches of bio-filter in a 9 inch deep grow bed.

When looking at the system as a whole in the short term, it really comes down to how much fish food is consumed by the fish on the input side of the equation and how much bio-mass (plants) you have in your system to absorb the nitrates on the output side. The measured quality of your water will determine how you are doing with feeding your fish if all other considerations have been properly designed into the system. Due to the accumulation of fish waste solids in the grow beds, it takes up to two years to realize if you have enough bio-filter to allow the solids to break down without over accumulation, as the fish are always in a changing state of growth and the amount of food given them changes over time. It is always good to have a higher grow bed to fish tank ratio than too little. Again, the plants are part of the bio-filter process and they are also in a state of growth.

Given the above, it is always best to have fish in various states of growth and plants that are planted at different times. This will insure the system will remain in balance over the long haul; for aquaponics is not a seasonal process, but a year round endeavor.

Another requirement for a successful aquaponics system is aeration. The dissolved oxygen levels, referred to as "DO", are very important. It has been shown in studies that DO levels of less than 3 parts per million cause considerable reduced fish growth, as much as half the growth rate of higher DO levels. DO is also important for the bacteria nitrification process. With DO levels of 6 or greater, your fish, bacteria and most plants will do markedly better than with lower DO levels. High DO levels can be accomplished by aeration of the water using both air stones and some kind of water jetting action. The jetting of water back into the fish tank breaks the surface tension of the water and allows the air, and therefore the oxygen in the air, to mix with it.

Also, many plants need oxygen on their roots for proper growth and this is usually accomplished by the ebb and flow, also known as flood and drain, process of the grow beds. This process deals with the continual flooding, adding of water, and draining of the grow bed. This allows the roots of the plants in the grow bed to be exposed to the air and thereby receive oxygen in a direct manner.