What is a Grow Bed?

The Aquaponics USA Food-Growing systems have two main components--the Grow Bed and the Fish Tank. That’s where all the action is taking place. It’s pretty easy to see the main 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 would do the trick and a real high powered microscope. The time-lapsed photography is easy (we’re constantly taking pictures of our Grow Beds across time). As for the microscope, we’re going to let an advanced Science Class handle that in the future while we describe here in words what’s going on in the Grow Bed that can’t be seen with the naked 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 waste into soluble nutrients that can then be available for use by the plants and the aquatic life. 



Aquaponics USA™ is pleased to announce we are the company featured on the Oekotau Aquaponics Website. Ockotau is a German company that makes a grow bed media called Hydroton, which they originally designed for Hydroponic growers. Clicking on the Oekotau link above will take you inside our greenhouse showing one of our earlier systems before our first planting. Hydroton offers the Aquaponic farmer even more rich surface area for a superior Bio-filter. Hydroton has a product page all its own on this site where you can purchase it at a great price.

The Grow Bed is a Bio-filter.

When the water is run 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 Nitrogen cycle. From this process, Nitrates are created, which 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?”: The Grow Bed is a Bio-filter.

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. This process is known as mineralization 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.

Aquaponics USA Grow Beds are Superior because we’ve added some real high-quality features to all of them. If you go to our product pages and look at the descriptors under Grow Beds, you’ll see the list. It says our Grow Beds are “Deep Media, Fully Supported, Bottom Insulated, Rapid Cycle with Highly Efficient Deep Delivery Water Rings”. So what does all that mean?

For starters it means a Deep Media Grow Bed is 12 inches deep as opposed to shallow-media Grow Beds that are about 7 inches deep. The advantages of Deep-Media Grow Beds are many. There is more media in them to cultivate a greater amount of the friendly bacteria necessary to convert ammonia from the fish waste into nitrates for optimum plant growth and allowing for higher fish stocking density. Due to their depth, these grow beds don’t need to be emptied and cleaned because the fish waste naturally breaks down as it migrates over time to the bottom of these deep Beds. This feature alone makes Deep-Media Beds a must.


Secondly, Fully Supported means a piece of 5/8 inch thick plywood is placed beneath every grow bed for added support; and these are strong, thick ABS Plastic or polyethylene Beds in the first place. The plywood sits on two support stands that are capable of holding five times the weight that will be in the Grow Bed. Then between the Grow Bed Bottom and that piece of plywood is a one half inch piece of polystyrene, which serves as Bottom Insulation.


Our new upgraded Grow Beds are Rapid Cycle Beds, which means they move the water in and out of the Grow Bed at twice the rate of traditional Flood & Drain Grow Beds. This provides lots of oxygen for the vegetable roots to grow stronger and faster. A Rapid Cycle Grow Bed also provides more life-giving oxygen to the bacteria for fish waste conversion, which allows for higher density fish stocking.


What about those Highly Efficient Deep Delivery Water Rings. Firstly, they’re making all of our Growing System photos obsolete because you won’t see these new water rings sitting on top of the Grow Beds as our photos show. These new Deep Delivery Water Rings are buried deep in the Hydroton where they deposit the water deep into the Grow Bed so the fish waste doesn’t accumulate at the surface of the bed. This allows for better distribution of the incoming water from the Fish Tank. There’s an observation spout that will be visible at the top of the Grow Bed so you can determine your siphon level and that your siphon is working properly. Otherwise, these Deep Delivery Water Rings are invisible.

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. Aquaponics uses 90% less water than traditional agriculture. 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 3 gallons of water. With 6 gallons of water in the system for every square foot of deep media 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 2 pounds of fish for every square foot of deep media 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 5 to 10 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 break 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 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. All of our Fish Tanks offer this Jet-Back feature.

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. Our new Rapid Cycle Grow Beds will increase this very important oxygen flow process.

Some folks building and selling aquaponics 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 leafy green 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 a Flood and Drain grow bed, use the numbers given above that have been proven to work.

Our Aquaponics USA greenhouse set up has three of our earlier systems in current operation in a five grow bed configuration 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. Our built-in float valve automatically signals the system to replace the water that evaporates out or that our plants up-take from it. The systems are stable and producing with minimal fish loss. Our 50 market-sized Tilapia are spread out between three 120 gallon tanks; and we have lost only a few fish, which happened shortly after the shock of transportation. In the years since then, the remaining fish have been healthy, eating well and growing. 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 up and operations and any other questions that will arise in starting up your system. We also support System Upgrades. We feel Tech Support is necessary for proper system operation and are offering it free.

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 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.

Here’s where you’re going to find more information on Grow Beds in action than you ever thought possible.

Here’s a great photo that was sent to us recently from one of our customers located in a Southern California city who bought four of our free-standing FAMILY/SCHOOL Series Grow Beds. He had his own fish tanks and just needed reliable Grow Beds to make his system complete. He referred to it as an “overgrown mess”. We think it’s beautiful. All this in just four Food Forever™ 11 sq. ft. Grow Beds.