This is section 2 of Part 3 in our “Key Elements of Water Quality.” Last time we talked about aeration and dissolved oxygen (DO). We covered the aspects of DO and the important role it has with fish, bacteria, and plants. I recommend that you go back and read that posting, Aeration - Section 1. Also, there are previous articles in this series - “Water Purity” and “Water Temperature.”
As stated before, we have covered DO, but now we want to discuss ways of adding oxygen to your system. Fish in their natural habitat, oxygen is supplied either by aquatic plants that produce oxygen through photosynthesis or from water movements such as waves and wind that dissolve atmospheric oxygen into the water. That can be the case in aquaponics to a minimal degree. Because of fish density and bacteria dependent upon DO, you must take extra steps to ensure your system has the proper amount.
Aquaponic growers that are a hobbyist and have less than commercial size systems have relative ease in supplying the proper amount of DO needed. In our e-book, “Step by Step Aquaponics, Simplifying the Building Process for You.” The systems we feature in the e-book takes proper precautions a grower must perform in providing DO needed for the fish, bacteria, and plants. Commercial systems can be much more complex for various reasons, but one being the stock density of the fish.
Today, we will talk about two ways to aerate your system and they are easy to perform. Under normal circumstances, you will not have any issues with DO unless you have a dramatic rise in water temperatures. If that is the case, the DO needs to be supplemented through management strategies.
In your system, you need to ensure that there is proper aeration in the fish tanks, bio-filter, and grow beds. By doing so, this will make sure that all forms of life are getting the required amount of DO, which is 5-8 ppm. Side note, I make sure my sump pit is receiving aeration. It’s an area you can capitalize on with little effort.
Two ways for aeration in smaller aquaponic units are to use water pumps to create a water flow, and to use aerators that produce air bubbles in the water. Water movement and aeration are critical components, and their importance cannot be overstated and stressed upon.
Water Pump Driven Aeration
Water pump driven aeration systems would include spray bars, venturis, oxygen saturation cones, and water mixers. Below is the description of each technique:
Spray Bars or Heads - are some of the most common ways to aerate your aquaponic system. It doesn’t require much skill in building them and they are easy to make. The main thing to consider is where you can place a spray bar to effectively break the water surface. In the designs we provide in our e-book, you will do so in the sump pit and fish tank. Below are the photos of the two ways we accomplish this. As you can see, we have a bar traversing across the fish tank. The water is sprayed directly onto the water surface. As it’s doing so, aeration is occurring. The other photo shows the water coming from the grow beds directly into the sump pit. The dump tube has a cap on the end and several perforated holes to allow the water to spray out onto the surface of the water. There are many ways you can customize a spray bar. The main objective is to break the water causing bubbles to form and water movement.
Venturis - are used to “suck” air into a pipe and mix it with water. Medium and high head pumps have enough pressure to allow installation of a venturi device which restricts water flow creating a suction force which draws air into the draft tube above the venturi. The flow of water and the pressure determines how much air can be drawn in. Please note it will reduce the water flow volume and pressure when using a venturi.
Spray bars or heads and venturis are really all you need in a smaller backyard aquaponics system regarding water movement (Note: you will need to add a mechanical aerator as well). There are other applications that can be used but not as common in the world of aquaponics or at least in the backyard builds, they are known as Oxygen Saturation Cones and Water Mixers. Click "READ MORE" in lower right to read the rest of the article.
Oxygen Saturation Cones - These are round, pot-belly fiberglass vessels which are designed internally to allow the water flow to slow while dropping down through the cone. This motion creates a continuous mixing of pure oxygen and water allowing supersaturation of oxygen into the water. Water flow is regulated on the outlet of the cone via a valve and short section of clear pipe. Oxygen gas is introduced upstream of the cone or in the cone’s neck and is regulated by a flow meter. The clear pipe allows inspection of the discharge water to ensure it contains zero bubbles. Dialing in the flow rate will allow for almost 100% efficiency.
Water Mixers - We can consider water mixers like a venturi, but they don’t use ambient air in the process. The mixers are designed to create a little back pressure so that the system water is mixed with water coming through the pipe to increase flow by as much as 5 times. Water mixers are relatively cheap and are easy to install. Because of the increased water movement, you can expect a small net gain in aeration.
One other thing to consider when building your system and this is by using grow beds with a medium such as clay pebbles or gravel. You may have a flood and drain system by using a siphon or timer to drain and refill the grow bed with water every 45 minutes. This of itself will cause aeration. As you drain the system, you are drawing air into the grow beds. Air will get trapped in the pockets of the medium. As the water rises, the air bubbles will turn into DO.
Diffused Air Systems for Aeration
Diffused air systems include those in which an air compressor of some type is used to provide compressed air to an air stone which is suspended down into the water. You need to ensure that you place a stone in your fish tanks and bio-filter; this is for a medium based aquaponics system. The 3 most common types of air compressors used are linear piston compressors, regenerative blowers, and rotary vane compressors.
Linear Piston Compressors - The most popular way to aerate for a non-commercial unit would be through these types of units. Not only popular but easy to attain online. There are some that can be expensive, but I have always purchased units for around $40. I have had great luck using them. They are low in wattage and relatively quiet.
Linear piston compressors produce even less air than both the regenerative blowers and rotary vane compressors but are quiet and energy efficient. They are useful for aerating small systems. Linear piston compressors can produce air for six 9” diffusers (stones) at a depth of 5’. Linear piston compressors will need to be rebuilt every 10,000 hours (1.1 years) of operation. The only downside to linear piston compressors is the small amount of air they produce.
Before we get into the final two diffused air systems. Unless you have a larger system that is more so borderline commercial, you will not have a need for these two types. This information will be good for you to know and have available in case you expand your system more so.
Regenerative blowers give an oversized quantity of air (volume) at low pressure. These styles of blowers are a superb alternative once needing air for a sizable amount of air stones or drilled pipe in applications shallower than four feet deep. They are an effective device in which a propeller blade is mounted to a motor shaft and therefore the propeller spins at a high revolution per minute developing large amounts of air. They historically can operate for periods up to five years with very little or no maintenance but only needing the air intake screen cleaned. The disadvantage of regenerative blowers is that they can only produce air 4’ deep. In applications deeper than 4’, the air stones must be raised, or a compressor must be considered in addition too.
Rotary vane compressors provide a medium quantity of air at higher pressures (4 -18 feet deep). These compressors are a sensible choice if air is required at deeper depths. An example application would be the aeration of a deep nutrient storage tank. The shaft from the motor connects to a spherical rotor with four slots. Carbon vanes fit within these slots and once the offset rotor spins, the vanes slide out against the outside wall and compress the air while forcing it out of the housing. They require maintenance on the vanes around nine months to a year. The disadvantage to a vane type compressor is the carbon dust that escapes the outlet, the price of the unit is compared to a regenerative blower, and the maintenance.
Remember to read the first posting regarding dissolved oxygen. It will make a clearer picture for you after reading these two articles. The rule of thumb is, you must have 5-8 ppm of DO or greater. Don’t worry about having too much, if there is an excess, it will dissipate naturally out of the system.
Buying test equipment for DO is possible. You can purchase a relatively inexpensive kit you may use during the peak of heat to ensure you are not losing too much oxygen. BUT the key is to watch your fish. Are they continually swimming close to the surface and trying to get air by taking gulps. This is one critical sign you need to respond to immediately.
One other item I want to discuss before closing, I highly recommend that you invest in a backup battery system that enables you to continue providing oxygen to your fish and bacteria. If your power goes out, you must be prepared for that. When I am talking about a power outage, I am speaking of a couple of hours to maybe max a day. BUT during that time, you need to ensure your aeration is still running. You can’t take a chance of having a fish kill. That is why myself, I have two marine batteries hooked together with an inverter and battery charger constantly keeping the batteries topped off. So, if the power goes out, you are ready to hook up the aeration pumps to the batteries. Yes, you can consider a small generator to have handy or even solar. It’s just how much you want to spend. Also, you must be ready in case an outage is longer than 12 hours because your back up battery will run out of power, eventually.
Make sure you subscribe to our blog and news before leaving today. Next time, we will be wrapping up this series on "Key Elements to Water Quality." We will be discussing the importance of testing your water for pH, ammonia, nitrites, and nitrates.
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