What Doesn’t Work:
Here’s a list of system components, techniques, and ideas for systems that we know don’t work, OR can have serious problems when applied on the commercial level, with some of the reasons why.
A. Media-Bed Aquaponics: This is growing aquaponic vegetables by running the system water through beds or tanks filled with different sizes and types of media (gravel, cinder, Hydroton, etc.), with the plants planted directly into the media. This is an example of something that works OK for a hobby or demonstration system, but does not work at all on the commercial level. We’ve tried it on a small scale, and it has tremendous drawbacks when scaling up.
We have reports from students in tropical and sub-tropical climates of media bed hydroponics working for a few months, then the bacteria associated with aquaponics clogging the interstitial spaces between the gravel bits, not only gluing them together, but also creating anaerobic decomposition zones that generate all kinds of nasty stuff that gets back into the aquaponics system and uses up all the system oxygen. As the system continues to clog over time, it gets less efficient at growing plants and keeping fish alive, and the media eventually has to be removed and washed or replaced. Media beds seem to work much better in temperate climates, i.e. Australia, and seem to work much better if they are flood-and-drain systems, but they still have the following drawbacks:
Planting into and harvesting out of media beds is a LOT more work than working with deep-water raft hydroponics, where you can pick up a lightweight raft and move it to a couple of sawhorses at waist level to do your harvesting and replanting, or even do this work sitting down, in the shade! Media beds are very heavy, and are either on the ground or are up at waist level on a really strong frame that costs far more money and labor to build than a raft system on the ground, around four times as much, by our estimate. It is more work (and takes more time) to pull a plant’s roots out of the gravel, and work to dig a seedling cube or a 2″ net pot with a seedling in it into the gravel. The funny thing? Lots of people claim there’s things you “can’t grow” in raft aquaponics. Well, that’s a photo of a banana tree and a pineapple plant in a 64-square foot Micro System below. We’ve grown everything else also and it’s just not true.
The biggest problem with media beds is that you have to go to them; they don’t come to you. What do we mean by this? You can never take a raft full of plants out of a media bed system and walk it over to a pair of sawhorses that is right next to your vegetable pre-chill tank (which is under a shade tent with a boom box for entertainment and your friends on the harvest crew to talk to) to harvest or replant. You have to go to wherever the media bed is located on the farm, out in the open, in the sun and wind, to do this work. It’s not much different from doing exactly the same thing in the soil, and removes many of the advantages of raft aquaponics.
It’s a really bad decision for a commercial aquaponics system, because anything that takes more labor can be the one thing that breaks your back during a particularly difficult year on the farm. You need everything to take as little time as absolutely necessary in order to make a profit and ensure the farm’s financial sustainability.
B. Nutrient-Film Technology (NFT) systems, although a standard in the hydroponics industry, and well-suited for a bacteria-free chemical hydroponic environment, have a few problem areas:
The small-size water delivery lines that deliver water to the hydroponic channels tend to clog badly with the bacteria and crud that thrives in an aquaponics system. If the water supply is interrupted by a pump failure or a clog that is not caught right away, the system can lose its plants very quickly as they dry out rapidly with no water reservoir below to draw on. This is prevented in a raft system, which always has deep water below the plants.
NFT systems usually involve more than one pump, which creates more potential failure points than our one-pump system. In our one-pump system you have about a week to correct a pump failure before serious problems start.
The infrastructure for NFT, with all the racks, movable troughs, and greenhouses (which are required so this stuff doesn’t blow away in a big wind) is much more expensive by our estimates than the aquaponics systems we use. One of our students has tried a modified test NFT system that we call a “thick” NFT system, with 4″ of water in the troughs, and a type of vertical rack system, and is growing strawberries in it. This system works well so far.
In addition, the plants are very sensitive to greenhouse air temperature because there is so little thermal mass in the thin film of water in the channels; this means that greenhouse air temperatures need to be much more tightly controlled than in deepwater raft aquaponics systems, resulting in much higher energy costs for those greenhouses containing NFT systems.
C. Fluidized Bed BioFilters/Mechanical Filters: Although designed for chlorinated swimming pools where the water is already pretty toxic to organic stuff, Fluidized Bed Biofilters have been used in aquaculture with some success. But, if they are loaded heavily enough and not back flushed hard enough or often enough, the sand or other media in them clogs and gets glued together by the system crud. They also generate anaerobic zones as in “A” previously. You may have to remove and clean or replace the sand, not to mention that these filters are expensive to buy and operate.
D. Bead biofilters using Kaldnes media, and rotating biological contactors (RBC’s) are expensive to buy, and don’t solve any problems that aren’t already solved in a deepwater raft system. These filters are needed in recirculating aquaculture systems to provide enough surface area for the nitrifying bacteria to live on. However, there is already so much surface area in our aquaponics systems due to the additional area in the troughs and on the bottoms of the rafts as well as that provided by the plant roots themselves, that there is no need to use these expensive filters to provide additional area for the bacteria to live on.
E. Ebb-And-Flow Aquaponics: This is when you flood an aquaponic bed (usually a media bed) or tube, getting all the plant roots wet, then let the water drain out again. There are timers and solenoid valves that work with your pumps to do this automatically (at least until a timer, pump, or solenoid fails and you lose a crop), or some fairly simple PVC piping arrangements that will do the same thing (until they clog and you lose a crop). Ebb and Flow has all the drawbacks of NFT combined with media beds: when there is a clog or a failure, everything dries out quickly and you lose a crop. There is also much more “stuff” to keep track of and keep free of clogs, which results in higher labor costs as well as higher initial construction costs. However, if your flood-and-drain system is run on bell siphons or some such device that doesn’t rely on timers and solenoid valves, AND the pipes used are large enough inside diameter to avoid clogs, this kind of system can work really well.
We experimented with media bed systems for awhile: we’d heard that some crops such as peppers did much better in them. However, we realized our raft systems grew peppers better, and only cost one-quarter as much to build. We found there wasn’t anything our raft systems couldn’t grow and ended up taking all our media beds down. See above photo of banana tree and pineapple plant in a 64 square foot raft system. Tomatoes, peppers, kohlrabi, mint, turnips and parsnips, green onions and leeks, strawberries and gardenberries, and many more things grow extremely well in the less expensive raft systems.
F. “Can’t I Just Raise Some Fish And Vegetables In My Pond?” Everyone wants to do it more easily and simply, so we always get this question: I have a tank (or pond) already, can’t I just put some fish in it and raise them? In a stand-alone fish tank or “pond”, the fish excrete urine and solids into the water. Because there’s no recirculating aquaponics system that cleans the water by converting this stuff into plants that then get harvested and taken out of the system, the urine and solids just build up in the pond until you get an algae bloom, i.e., a whole lot of phytoplankton taking advantage of the nutrients in the water.
When algae blooms, the result is a high DO level (dissolved oxygen) in the daytime because of all the algae photosynthesizing and creating oxygen. Oxygen is good for the fish, but algae isn’t, because there is a reverse cycle in the dark of night (Diel cycle) that is caused by the die-off and decomposition of the phytoplankton, and other nightly oxygen uses. The nightly die-off of phytoplankton consumes much or all of the oxygen made by the algae in the daytime, which reduces the DO level, sometimes to dangerous levels. The DO can easily go so low it stresses the fish at night, which means they grow poorly and may not reproduce at all. Some of these stunted fish may manage to breed, and some of the fry make it to very small adult size. What this means is that without a biofilter similar to an aquaponics system connected to it, or a whole lot of water being flushed through it daily, a tank or pond will have a lot of algae and just a few 7″ to 8″ long tilapia in it after a year of operation.
So after you answer that one, people ask, “Why can’t I just put some vegetables in a raft on top of my pond/tank?”If you manage to put plants in a floating structure on top of your pond or tank, and you manage to protect their roots from getting eaten by the fish, then you will have about five percent of the area in plants that you need to really clean the water to acceptable quality for the maximum amount of fish you could raise in that volume of water. This is also assuming that you have enough water movement and aeration (which, by the way, your pond or tank ALSO doesn’t have, and you need to provide). So you either need to add water pumping and aeration to your fish tank or pond, OR reduce the amount of fish to the point there is no appreciable production from your tank, either vegetables or fish.
It’s a lot easier and much more productive just to build a shade cover for your existing tank, then build a couple of hydroponic troughs and connect it to them; with a water circulation pump and an air pump or blower for getting oxygen to your fish and plants. You need the shade cover to keep the tank from growing algae, which will use up all the nutrients in the water and prevent your vegetables from growing well (or at all). You need the troughs so you can have enough area of vegetables to clean the water of fish effluent (nutrients for the plants), which is about 10-20 times the area of your fish tank. You’ll get decent production of both without the problems incurred trying to do both in one container.