Deep water culture aquaponics is a system where plants grow on rafts placed over an aerated and nutrient-rich fish tank. The plant roots float in the pool of water, and no media is used to filter the solid waste. Instead, a filtration system is set up to support the cycle.
Deep water culture aquaponics has the benefit of providing better temperature and nutrient stability. It’s highly productive, easy to monitor, and allows for wider root expansion. However, it has high setup costs, high filtration demands, and takes a lot of space.
The benefits of deep water culture aquaponics far outweigh its drawbacks. This article will take an in-depth look at its pros and cons and at a few other things you should know about DWC.
The Pros of Deep Water Culture Aquaponics
Deep water culture (DWC) aquaponics combines aquaculture and hydroponics. The fish tank and grow bed are interconnected with a pump and pipe, where water from the fish tank flows to the grow bed.
Once it’s purified by the plants, the water flows back into the fish tank. Unlike other aquaponic systems, the grow bed in DWC is at least 1 ft (30.5 cm) deep and is filled with water.
Here are the pros of deep water culture aquaponics:
Water Temperature and pH Levels Are More Stable
Compared to other aquaponics systems, DWC requires the largest volume of water. Because of this, the external temperature doesn’t easily interfere with the water temperature. This helps control temperature and pH fluctuations.
Consider a small pool and a large one on a hot day. The water temperature in the small pool is likely to be warm, but the bigger pool will be cool and more stable.
Maintaining ideal pH levels for plants, bacteria, and fish in aquaponics is difficult, so having a system where the water’s pH doesn’t alter much is a plus. The ideal PH for a DWC system is 6.8 to 7.0.
Changes in pH levels in aquaponics systems happen when bacteria break down fish waste into nitrates. Water tends to become more acidic during this process. The large water volume of the tank counters acidification, so the water pH stays relatively stable.
Watch this YouTube video if you want a visual demonstration of the pros of the DWC aquaponics systems:
Ideal for Plants With Deep Root Systems
The grow beds in DWC aquaponics systems vary in size, but the minimum depth should be at least 1 ft (30.5 cm). When the conditions are ideal, plant roots grow vigorously and deeper than in other aquaponics systems. This makes DWC systems ideal for larger plants. However, this is only possible if the grow bed is well aerated.
When setting up a DWC aquaponics system, oxygen is a component you shouldn’t overlook. Plants need oxygen for cellular respiration, while fish need it to breathe.
Unfortunately, water doesn’t have sufficient oxygen to support plant growth 24/7. In DWC, this challenge becomes even more complex because of the high water volume and the full immersion of plant roots. Water will be the main source of oxygen for your plants.
When dissolved oxygen is low, fish, plants, bacteria, and other aquatic organisms won’t survive.
In the aeration system of DWC, dissolved oxygen is pumped through the water and absorbed by the root system. You can use air stones or an air pump to introduce air bubbles into the grow bed.
Air pumps or air stones allow you to equally distribute the oxygen across all your plants, even if you have a large grow bed. Air stones and air pumps have different airflow capacities, so choose the one that works best for your aquaponics system.
Easy To Scale
It’s easy to expand a DWC aquaponics system from a domestic to a commercial operation. For commercial farmers, scalability is just as simple. DWC systems it’s easy to include new plants or add more of the same.
If you have a lot of expansion space available, you can add more grow beds and fish tanks. Alternatively, you can get a bigger fish tank and a larger grow bed. As you can see, DWC aquaponics isn’t only easy to scale: it gives you the freedom to decide how to do it.
That said, if you’re just getting into DWC aquaponics, it’s best to start small and only expand when you have mastered this method. Sometimes plants can fail to grow if you introduce them to the system too early. You won’t take any big financial risks and you’ll remain able to expand whenever you want.
This YouTube video gives in-depth guidance on how to scale DWC aquaponics systems:
Plants Grow Quickly
Plants in a DWC system usually grow quickly. Their roots are fully suspended in water, which gives them a regular oxygen supply. Nutrients from the fish tank are also in abundance.
Since this system doesn’t use any media, plants don’t suffer from space restrictions, which means the roots grow as deep and wide as they can go. It’s estimated that plants grown in aquaponics systems grow up to 25% faster than those grown in soil.
For example, tomatoes grown in DWC aquaponics start flowering four weeks after planting, and they’ll be ready for harvest after two months. This is a relatively shorter time than tomatoes grown with conventional methods, which take 60 – 100 days, depending on the variety. Lettuce takes 30 days to mature in DWC, which is half the time it takes for it to mature in soil.
Comparing Plant Growth to Maturity in DWC Aquaponics, Hydroponics, and Soil
| Plants | DWC Aquaponics | Hydroponics | Soil |
| Tomatoes | 8 weeks | 8 weeks | 4 – 5 months |
| Cucumber, Zucchini, and Squash | 8 weeks | 6 – 10 weeks | 10 – 12 weeks |
| Basil | 4 – 6 weeks | 4 weeks | 8 weeks |
| Lettuce | 3 – 5 weeks | 4 weeks | 6 – 8 weeks |
| Cabbage | 11 – 26 weeks | 15 – 17 weeks | 30+ weeks |
Plants grown in DWC aquaponics systems mature at about the same pace as those grown in hydroponic systems. However, some plants, like cabbages, mature faster in aquaponic systems than both hydroponics and soil.
Harvest cycles in DWC aquaponics systems are also longer. For example, tomato harvest cycles can last 8 – 10 months, and they start only four weeks after planting.
Most garden tomatoes produce fruit for three months. DWC aquaponics has the edge here, not only because tomato plants start producing early, but because production lasts longer. Additionally, garden tomatoes are more susceptible to pests and diseases, which compromises the yield.
Low Maintenance Costs
The upfront costs of DWC are high, but once the system starts running, the maintenance costs are actually very low.
Once you have invested in all the key pieces —fish tank, grow beds, sump tank, filters, air pump, air stones, and plants—, the only upfront cost that remains is the labor needed to set up the system.
Once the system is up and running, your money will mostly go to water, electricity, and fish food bills.
Higher Yields
DWC aquaponics systems have higher success rates compared to traditional farming methods. And because fish and plants are produced together, DWC systems are even more productive.
Plants mature much faster than fish, so you can have multiple plant cycles before the fish mature.
These advantages have pushed many organic farms to invest in DWC aquaponics.
According to the US Department Of Agriculture (USDA), the demand for organic food has grown steadily over the years. In 2008, 11,000 certified farms were producing organic food. By 2019, certified organic farms had grown to over 16,500 farms. IndustryARC estimates the global aquaponics industry to be worth $1 billion.
The yield of plants grown using DWC aquaponics is 30% higher than traditional farming methods. Resource management is also much more efficient, with plants grown in DWC aquaponics using only 10% of the water in they would need in traditional farming methods.
Additionally, a DWC system can yield as much as soil farming while covering approximately 10% of the land.
Easy To Monitor
Monitoring DWC aquaponics systems is fairly simple. However, you need to do it frequently and know what to look for when examining the water, plants, and fish. When checking DWC systems during each plant cycle, you need to:
- Regularly check the pH levels and confirm they’re between 6.8 and 7.0. If the water pH is too low, you can raise it by adding calcium carbonate and potassium carbonate at a 1:1 ratio. If the pH is too high, you can use nitric, phosphoric, or muriatic acid to lower it. Add the acid little by little until you achieve the desired pH.
- Check the dissolved oxygen levels occasionally. Dissolved oxygen levels are usually lower when the water is warm. But because water temperatures don’t fluctuate, DWC aquaponics systems have a stable oxygen supply. Fish tanks with plenty of fish also have lower DO concentrations than tanks with fewer fish. The ideal DO level is 5ppm or higher.
- Monitor the water temperature. The temperature fluctuations will affect plant growth and the fish. Fortunately, the temperature in DWC systems is fairly constant because of the large volume of water. However, you should keep checking the temperature in the fish tank to ensure it’s ideal for the survival of the fish you have stocked. For example, a water temperature of 65 to 85°F (18.33 to 29.44°C) is ideal for goldfish, tilapia, and bass.
- Regularly check ammonia levels in fish tanks. Avoid overfeeding the fish and putting too many fish in the fish tank because this will increase ammonia levels significantly. High ammonia levels are toxic to fish. Low ammonia levels will affect plant growth because it signifies low production of fish waste. Increase ammonia levels by giving the fish more food, increasing the number of fish, or using a smaller fish tank.
- You should also monitor nitrate levels. When bacteria break down fish wastes into nitrates, the plants should absorb the nutrients. High nitrate levels signify an imbalance between fish stock and the number of plants. You may need to add more plants or increase the number of grow beds to increase nitrate uptake.
A key part of monitoring your aquaponics system is having the right tools. If you can’t measure correctly, you won’t be able to regulate your DWC’s delicate environment. Be sure to get specific tests kits for dissolved oxygen, ammonia, and nitrate levels, available at your local aquarium store or online.
Although you need several monitoring systems for DWC aquaponics, most tests don’t take more than a few minutes, and you get results in seconds. You don’t need to carry out the tests daily, which means you have the flexibility to monitor the systems whenever you can.
Minimal Risks of Plant Diseases
Since the raft blocks the plant stems from coming into contact with water, plant diseases become minimal. Water droplets on the stem and leaves increase the risks of plant diseases—bacteria and fungi spread easily in moist conditions.
Aquaponics also shares an anti-disease advantage with hydroponics: because the plants are in a controlled environment, the chances of pests appearing are minimal. Most pests come through contact with dirt, but aquaponics lacks soil or any other kind of medium.
Even if pests manage to appear, they’ll be much easier to deal with compared to traditional farming. Because the plants are inside an enclosed space, you can resort to non-invasive methods like introducing natural predators.
The Cons of Deep Water Culture Aquaponics
Like other aquaponics methods, DWC systems have its drawbacks. But don’t get the wrong idea: the pros far outweigh the cons, and this system remains the superior choice for both small and large-scale operations.
These are the cons of deep water culture aquaponics:
DWC Needs Additional Filtration of Solid Wastes
Grow media usually work as mechanical and biological filters. Media in other aquaponics systems, like gravel or stones, captures and contains solid fish wastes, which break down over time. Waste is eventually absorbed by the media and ultimately by the plants.
Grow media also provide biological filtration. Bacteria grow around the media, breaking down solid wastes into nitrates, which the plants absorb.
Since DWC systems don’t use grow media, you’ll need to introduce a filtration system. Without filtration, the solid wastes will attach to plant roots and block nutrient uptake.
Additionally, wastes may block the pumps and pumping components. Wastes will also create anaerobic zones, which will prevent bacteria growth. As we just explained, these bacteria are crucial for the nitrification of the wastes.
Incorporating filtration systems in your design will help keep the water safe and healthy for the plants and fish. The issue is that this adds costs to any setup of DWC aquaponics.
Plants Die if the Air Pump Fails
If the air pump fails, you have a small window to replace it. Since the plants depend entirely on dissolved oxygen, they can’t go for long without the pump. This is one of the reasons you should be regularly monitoring your DWC system. As soon as you notice the pump isn’t working, replace it immediately.
If you take too long to replace the pump, the plants will start wilting and algae will start growing in the fish tank. Algae in aquaponic systems will cloud the system, clog the pipes, and deplete oxygen levels in the water.
Water pH and Nutrient Levels Fluctuate in Small Systems
Water pH and nutrient levels in DWC aquaponics systems are usually quite stable, but this is only true for large systems. In small aquaponic systems, water pH and nutrient levels fluctuate wildly.
The fish waste concentration is higher in small fish tanks. The bacteria may not break down the solid waste as quickly as it would in a larger tank, which means the concentration of nutrients will be high and alter the water pH.
Watch this YouTube for an analysis of fish tank vs grow bed ratio and how to avoid pH and nutrient fluctuations:
Some Large Plants Can Be Difficult to Control
High nutrient plants, like tomatoes and cucumbers, are ideal for DWC aquaponics. However, controlling such plants can be difficult in large aquaponic setups. These plants can also be quite heavy. When monitoring the grow bed, lifting the raft can cause the stem to break.
Still, the difficulty isn’t much higher when compared to other hydroponics or aquaponics systems. Besides, these plants also happen to give the best financial returns.
DWC is a Breeding Ground for Mosquitoes
DWC aquaponics systems end up with a large volume of stagnant water, so it’s not surprising to see mosquitoes turn it into their breeding ground. Change the water once every two weeks to keep this from happening.
To avoid shocking and endangering your plants, you should top up the grow bed once or twice before pouring out the water and replacing it with fresh water. This won’t only help your plants, but it’ll also help control the mosquitoes.
The Best System for Aquaponics: What To Consider
Although DWC aquaponics has more pros than cons, it’s not ideal for every case. Before deciding on the type of aquaponics system you’ll set up, consider the following:
- Location. The location of your aquaponics system will determine if it’ll be successful or not. If indoors, ensure the area is easily accessible, and the space is close to a water source. If the system is set outdoors, ensure the system will be safe from predators.
- Space. Whether using DWC aquaponics, nutrient film technique, or media beds, you need to check if the system has enough space. Consider how much you’d like to be able to scale in the future.
- The plants you intend to use. When it comes to aquaponics systems, some plants are more suitable for one setup than others. Media beds are versatile and accommodate different plants, such as tomatoes, cucumbers, and peppers. DWC aquaponics systems are ideal for leafy vegetables, like lettuce, chard, basil, mint, and kale.
Before settling for a DWC aquaponics system or any other type, make sure the system fits with your plans. All aquaponics systems are high-yielding, but some systems are costlier than others. Compare the pros and cons before deciding on the system that works best for you.
Final Thoughts
DWC aquaponics has its benefits and drawbacks, but the pros far outweigh the cons.
In the end, for the system to work successfully, you need to plan appropriately. Don’t just think about how you’ll get it to work today: consider possibilities for expansion.
Since you’re balancing plant life, fish, and bacteria, you need to make sure the environment is delicately controlled. For that, you’ll need the right equipment and the right design.
