Hello, growers! Consider this your bare bones guide to understanding and building a simple Aquaponics system. There is much more to cover than this brief overview, but it should help you better understand how cannabis grows in Aquaponics. Using this technique, we’ve been able to grow some great, high-yielding plants. The one pictured above we grew using Aquaponics and measures almost nine feet across.
You can purchase a turn-key aquaponics system kit or build one from scratch. To properly grow cannabis, we are going to set up our system to function by flood and drain. To do that, your water pump will need to function on a timer.
First, drill two holes in the grow bed that will fit two bulkheads, one for the fill and one for the drain. Next, place your fill and drain into the bulkheads and connect the pump. Plug the pump into the timer and set it on for 15 minutes and off for 45 minutes. This is a far more frequent flood cycle than in hydroponics but remember the water needs to be regularly filtered for the fishes’ sake.
Place your now-plumbed grow bed over your fish tank and fill it with the grow medium of choice. At AquaponicsSource, we really like round, expanded clay media because it’s easier on your hands and lasts a long time. We like to see at least 12” of depth on the grow bed so it adequately filters the water for the fish.
Next you will cycle your system before adding fish. Cycling is the process of establishing a colony of bacteria that can carry out the nitrogen cycle in your system. The bacteria start with the ammonia in fish waste in covert it step-wise into nitrate fertilizer, which can get taken up by the plants once you put them in.
It is important to cycle your system before planting. Without cycling you will not have enough beneficial bacteria to provide your plants with the nutrients they need. To tell if your system is cycled you need to test your nitrogen levels starting with ammonia. You want to use pure ammonia, or an AquaCycle fish-less cycling kit, and bring your ammonia to 4 ppm. Anything much above a 4 ppm will start to kill bacteria, but start with at least 2 ppm.
The next spike in the nitrogen cycle you will see is nitrite. This will spike as bacteria convert ammonia into nitrite. Finally the nitrite is consumed and turned into nitrate. This is the form of nitrogen most available to the plants in your system. You know your system is cycled when your ammonia and nitrite read 0 ppm, or close to it, and your nitrogen is all converted into nitrates. Read here for more information about cycling.
Once your system is fully cycled, you can now put your fish and plants into your grow. It’s useful to continue to monitor your system until you’re sure a good balance is reached between the plants, bacteria and fish.
The Dual Root Zone
With a traditional Aquaponic setup, you will still have issues getting nutrient levels high enough just with what is provided by the fish and microbes. They provide a lot of what’s necessary—but not 100% of what we need. With just the nutrients from the fish, we are still a little short on potassium and phosphate. So to get around, this we use something called the dual root zone planting method. This is the key to growing cannabis successfully in Aquaponics.
In a dual root zone you separate a layer of traditional expanded clay media with a layer of burlap, or other root permeable material, and add a soil layer on top. This dual root zone allows you to house your terrestrial microbes in an upper soil layer, which can be amended however you’d like, and aquatic layer to house your aquatic microbes. This allows you to have some longer-term nutrient retention in the upper root zone while allowing great gas exchange and water to your plants at the same time. It also enables you to gain the benefits of both biomes of microbes and maximize natural nutrient input going into your plants.
Once you know the amount of water the soil layer can hold, you can water this layer separately with phosphate and potassium rich organic fertilizer without fear that it will contaminate the fish water. Too much phosphate and potassium is unhealthy for the fish and microbes, but is necessary for flourishing plant growth.
Additional benefits of the dual root zoning method have been seen in our testing. We haven’t had an issue with cannabis plants yet, and lab tests done in other parts of our company have noticed that dual root zone grown tomatoes have higher resistance to powdery mildew than tomatoes grown in regular clay media. The other big benefit to you and your wallet is that you only need to supplement the water and soil in small amounts meaning much less fertilizer gets used overall. The plants also barely need to get flushed before flowering. In a dual root zone your plants are getting supplemented in the soil layer but their main source of water is always the nutrient rich water the fish live in. When you are about three or four weeks out simply stop supplementing and let your plants flush with the water from your Aquaponic system. This leaves you with an amazing, clean, rich, smooth flavor with no harshness to speak of.
With Aquaponics we have five knobs we can turn to adjust our available nutrients. You can supplement using fish safe additives directly into your sump tank or fish tank. You can supplement by changing the diet of your fish, or the frequency or amount of feeding, to increase output of desired nutrients. You can add soil amendments of your choice to the soil you use for your upper half of the root zone pot. You can use any liquid supplement you desire in the upper root zone at any time during growing. And lastly, you can foliar spray if you also choose. This gives you a wide range of options when you want to supplement your plants. We have done a lot of work towards figuring out what works best in each application. You can learn all about it over at PotentPonics.com. We have everything from classes and education into so-called turn-key systems.
Thanks for taking the time to learn about Aquaponic growing, and we hope you give it a chance. We know you won’t be disappointed!