Aquaponics at The WSCU Pinnacles Greenhouse
December 10, 2012 § Leave a comment
By Kyle Brookens
Aquaponics is a closed-loop system that generates an abundance of produce, and it seems to twinkle with an inspiring aesthetic. The system is not perfectly closed-loop, for there are many start-up inputs, and you must have a continuous supply of fish food. As far as raw materials and resources go, aquaponics requires the following: grow beds (wood and EPDM pond liner, or plastic), screws, pipe brackets, the tools to build the system, a fish tank (glass, wood and pond liner, or plastic), a magnetic submersible pump, PVC pipe, a heater with a thermostat (depending on location), PVC fittings, bulk head fittings, fish food, fish feeder (not entirely necessary), Hydroton clay pellets or lime-free gravel, an API master freshwater test kit, a de-chlorinater, air stones, PH up and/or PH down (if you have too high/too low PH readings), seeds, fish (tilapia, coy, goldfish, or trout) nitrosomonas (bacteria), nitrospira (bacteria), some red worms, water, property, and electricity. As you might infer from the list of materials and resources, the system is far from a perfect closed-loop operation, and it is also far from simple. Regardless, aquaponics mimics natural processes and is an excellent demonstration tool for education. Aquaponics also has major implications in regions where water is scarce. Besides that, Aquaponics is a new and fun way to grow your own food.
There are a few different types of aquaponic systems and each have their pros and cons. There are commercial lilly pad farms, flood and drain (ebb and flow) Constant Height One Pump (CHOP), Nutrient Film Technique (NFT), Constant Height in Fish Tank (CHIFT), Pump In Sump Tank (PIST), two pump, Barrel, and IBC tote bed systems to name a few (Dusty Szymanski). I am only familiar with flood and drain and CHOP systems, for I believe that these systems work well on the scale that I am working with. CHOP systems are great because they allow the water in the fish tank remain at the same height. This system is ideal for both plants and fish, because it does not lower the level of water in the fish tank and it allows the grow beds to flood and drain with the use of a bell siphon. The bell siphon allows the grow beds to fill to the height that you desire, then as soon as the water starts to flow into the pipe, the bell siphon creates a vacuum, and therefore, drains the bed completely. The fish tank remains at a constant level in this system because it requires the use of a sump tank. The grow beds will drain into the sump tank and the pump will continuously pump the water from that tank into the fish tank. This system is also great because it prevents your pump from being clogged with fish emulsion. On the downside, it is more beneficial for your bacteria and your plants to have the pump on the bottom of the fish tank so all the ammonium resting at the floor of the fish tank gets cycled without doubts. This is where a flood and drain system trumps the CHOP system, but not by much. The Western State Colorado University’s Pinnacles Greenhouse has a flood and drain system. It is exactly the same as a CHOP system, except there is no sump tank and the grow beds drain directly into the fish tank. The pump rests on the bottom of the fish tank and less materials are used because the sump tank is excluded. The simplicity of a flood and drain system is also a benefit, but as I stated before, there really is no perfect aquaponics system, each has pros and cons.
With any aquaponics system, it is important to know a few key pieces of information. First, it is important to make sure that the grow bed to fish tank ratio is at least 1:1. If this is not possible, it is better to have a system that has a greater grow bed to fish tank ratio. The more plants there are, the more filtered the water will be for the fish, because there is more surface area for bacteria to grow and more plants will absorb more nitrate. The bottom line is that the fish need to be happy. It would be better to add seaweed fertilizer for your plants than to have your fish choking on nutrient rich water (this would only be necessary when the plants are fruiting anyways). It is also important to add water to the system sometimes, for it will loose some water via transpiration, evaporation, and photosynthesis. How much water the system needs just depends on the season and how much water is being used by the plants and fish. The pump is an extremely important piece of the aquaponic puzzle because it keeps everything in motion. The pump is so important that it is recommended to have at least one back-up pump, just in case it fails. As a rule of thumb, one cubic foot of grow bed space equals seven and a half gallons of water. If the fish tank size is 300 gallons, the grow beds need to hold 40 cubic feet of water (300 gallons/7.5 gallons=40 cubic feet). This is a simple way to calculate the 1:1 ratio, for the grow beds should be about 1 foot deep. The amount of fish required by the system also depends on the amount of water in the fish tank. On average, the system should have one pound of mature fish per 5-10 gallons of water. A mature tilapia fish weighs about 1.5 pounds. In this case, a 300 gallon fish tank has a maximum carrying capacity of about 30-60 tilapia (5-10 gallons of water for each fish/300 gallons = 30-60 fish) . In terms of pounds of fish produced, a 300 gallon tank in about 9-12 months will render 45 – 90 pounds. All things considered, it would be best to shoot for the mean of the two and stock the tank with 45- 50 fish and produce about 70 pounds.
When cycling begins and when the system is up and running, there are five things to test once every week: PH, nitrite, nitrate, ammonia, and temperature. When starting the system from scratch (cycling) it is important to test the water every day. This is where the API master freshwater test kit and the fish tank heater come in handy. Fish prefer the water to maintain a PH of 6.5 – 8, the plants prefer 5 – 7, and the bacteria and worms prefer 6 – 8. Overall, the system is running well if the PH is between 6.8 – 7. It does not have to be perfect, but the goal is to maintain that PH level. If there is ever a problem with the PH level, add the hydroponic PH up or down, as needed and directed (whenever adjusting PH, do it slowly, at .2-.5/day). Blue tilapia prefer temperatures between 75 – 80 degrees Fahrenheit, plants prefer about the same temperatures, and the bacteria prefer temperatures between 77 – 86 degrees Fahrenheit. Temperatures around the low 80’s will keep everyone happy. If the system is too rich in nitrites (NO2), than something is usually wrong with the nitrospira bacteria. If the system is too rich in nitrates (NO3), than the plants are not absorbing enough nutrients, or the plant density is too low. If the ammonium (NH3) levels are high, than something is wrong with the nitrosomonas bacteria, or the water temperature is a little too high. There is no perfect solution to these problems, but for the bacteria issues, it is worth purchasing some Cycle, Stress-zyme, Bacta-Pur, or proline nitrifying bacteria, or getting a sample from another mature aquaponic system. Nitrates are nearly harmless to the fish, but ammonia is quite toxic and nitrite is very toxic if the levels are too high. A rule of thumb is to have high nitrate concentrations and low (below .5) ammonia and nitrite concentrations. Table one shows the maximum long-term amounts of ammonia levels that is considered safe at a given temperature and PH (theaquaponicsource.com). If the ammonia levels exceed the levels in this chart, the aquaponics systems needs a flush. A flush requires that 1/3 or more of the water must be pumped out and replaced with fresh de-chlorinated water. If the nitrite concentrations are too high, flush the system, consider adding non-iodized salt, and stop feeding the fish until the nitrite level gets below 1. It is also a good idea to aerate the water with air stones and air pumps as much as possible, because nitrite is the equivalent of carbon monoxide to humans.
A good resource for aquaponics is Sylvia Bernstein’s Aquaponic Gardening book (about $20 USD).
|Maximum Ammonia Levels (ppm) Based on Water Temperature|