Bullet-Proofing Your Aquaponics System In this section, we look at the common causes of failure associated with running an aquaponics system...and how to prevent them. An Aquaponics Nightmare Consider this scenario. It s the day before you harvest the first fish from your very own aquaponics system. For the past nine months, you ve fed and tended them night and day and you ve watched with pride as they ve grown from 25mm fingerlings to the sleek 350mm beauties that glide effortlessly around the tank. That night, as you dream of lightly steamed freshwater fish with a sprinkling of soy, spring onions and shredded ginger, a transformer in a nearby substation explodes. At that instant, your pumps and aerators cease operating. While it is a common enough occurrence, and the local power utility is able to change the transformer, it will take several hours to complete the work and to restore the power supply. Meanwhile, you sleep on, oblivious to the drama that has just begun to unfold down in your fish tank. Since the water is no longer circulating through your biological filters or grow beds, ammonia and nitrite levels creep higher as each hour passes. Of course, that's much less of an issue than the fact that, because of the weight of mature fish in your system, the dissolved oxygen levels in the water will have begun to plummet..particularly since your air pump also ceased to operate at the instant that the power was interrupted. After five hours, the linesmen from the power utility radio their supervisor to advise that the new transformer is ready for service. Another fish gives a final feeble kick and dies; the tenth such passing within the past 15 minutes. The rest of your fish are in various states of distress. Some are swimming on their sides while others gasp at the surface of the water. You ll later reflect on the cruel irony that fish can die from the lack of air while their head is out of the water and their mouth is wide open. Three hours later, you spring out of bed and pull on your clothes. You re experiencing a sense of excitement as you stride into the shed but your exhilaration turns to dismay as you begin to comprehend the devastation that has occurred in your fish tank. Later that morning, as you shovel dirt over your dead fish, you reflect on what you might have done
2 to avoid the whole sorry business. Now, it makes me feel uncomfortable relating that story, but I know several people who have first hand experience of a major fish kill and, while they eventually rationalise their situation, they aren t happy campers at the time that it happens. Realistically, the risks that confront backyard AP operators include: Power failure Equipment failure Ammonia or nitrite toxicity Leaks or bursts Fish disease Power Failure Power failure is one of the most significant risks confronting your aquaponics system. Any interruption to the power supply will mean that your air pump will no longer be aerating the water in the fish tank. Falling Dissolved Oxygen (DO) levels is the most immediate threat. The water in your system is no longer recirculating through your bio- filter or grow beds so, depending on the duration of the blackout, rising ammonia levels will also become an issue. Once dissolved oxygen levels drop below a certain point, your fish will become stressed. As the DO level drops further they will begin to die. How quickly your system reaches a critical point depends on stocking levels. Obviously, a tank with 1kg of fish in 1000 litres of water will remain in better shape for longer than the same tank containing 30kg of fish. Power failures that occur at night pose the greatest threat because they may go for hours without you being aware of the problem. The first outward sign that anything is wrong may be lots of dead fish. Power failure is not the only prospective drama: human error can play a role, too. On two occasions, I ve left my pumps switched off following operating maintenance. While my fish were small enough (and the stocking rate low enough) that they survived, the same could not be said for the plants in my gravel grow bed. Several hours in the hot sun without water left them looking decidedly sick. These latest of these two episodes prompted an immediate search for an effective automatic back up system. A good fail- safe back up system comprises: Back Up Power Switching Relay 12 volt car or truck battery (a deep cycle battery would be even better)
3 Battery charger 12 volt water pump we've found small marine bilge pumps to be suitable for this purpose. 12 volt air pump The Power Switching Relay is a switch which, while 240- volt power is available, is open. As soon as the 240v supply is interrupted, the relay closes and 12 volt power flows to the 12 volt back up water pump and aerator. Once the 240 volt power supply is restored the relay opens and normal 240 volt pumping and aeration resumes. This little system is sufficient to carry a small aquaponics unit overnight. In the event of an extended power failure, it gives me time to organise a more robust solution like a generator. The incorporation of a similar back up system into your aquaponics unit is a wise investment. If you end up with several tanks, you will find it more cost effective to install an alarm that alerts you to the fact that the power supply has failed. This will enable you to start up a generator to power your pumps and air blowers pending the restoration of normal power supplies. Equipment Failure When it comes to buying pumps, you get what you pay for. Cheap pumps are false economy. Using two small pumps in your system (rather than one larger one) will help to avoid the consequences of pump failure should it occur. While one pump won t keep your system going forever, it will sustain it long enough for you to discover that the other pump has failed. Importantly, your fish will have survived. Similarly, the use of an air pump in your system will help to keep things going for a while in the event of a water pump failure. Ammonia or Nitrite Toxicity The risk posed by ammonia or nitrite toxicity, is that it will damage the fish gills or even kill them. The best way to prevent ammonia or nitrite toxicity is not to allow the levels to reach toxic levels in the first place. Increased ammonia levels usually happen over a period of days. If you become complacent around water testing, you can expect to experience periodic ammonia toxicity. If you suspect ammonia or nitrite toxicity, conduct a full battery of water tests and suspend feeding immediately. If the tests confirm high ammonia or nitrite levels, replace enough water to bring the water quality back within the appropriate parameters. Monitor the system closely until it stabilises. Leaks, Bursts and Blockages
4 If you develop a bad leak, or a pipe breaks, you may eventually lose all of the water in the fish tank - with catastrophic consequences. The impact of this risk can be minimised by incorporating float switches into your system design. If the water level drops below a certain point, the float switch will stop the pump. Of course, if this situation goes unnoticed for too long, the Dissolved Oxygen will drop below acceptable levels so float switches should be used in conjunction with a low water alarm. On two occasions, I ve come close to disaster because of blockages. A bulkhead fitting that allowed water to flow from my fingerling tank back into the main fish tank became blocked. This caused the fingerling tank to overflow and to gradually empty the main tank. Both times, the blockage was caused by fingerlings becoming trapped in the bulkhead fitting. The root cause, however, was human error. I had forgotten to replace a strainer that would have prevented the fish from entering the fitting in the first place. Fortunately, I discovered the dramas before they resulted in a fish kill - sheer luck! Suffice to say, my interest in float switches and alarms intensified following the more recent of these two episodes. Fish Diseases While an exhaustive discussion of fish diseases is outside the scope of this manual, the one that has affected several of my aquaponics colleagues is ICH. The most common disease of freshwater fish, ICH (pronounced ick) is a protozoan disease that is often called 'white spot disease. The causative agent is Ichthyophthirius multifiliis. Some people believe that ICH is present in all captive fish populations and that, when fish become stressed, their immune system becomes less effective and an outbreak of ICH can occur. While microscopic examination is the only conclusive way to confirm the presence of the disease, symptoms of ICH include: White spots (the size of a coarse grain of salt) on the body and gills Agitated fish movements Rubbing against objects in tank (flashing) Loss of appetite If the disease goes untreated the symptoms may progress to respiratory stress, severe agitation and eventually death. The life cycle of the ICH agent is complicated but the important thing to remember is that the condition can only be treated effectively at a particular stage when the ICH organism has left the fish and is preparing to multiply and attach to other fish. It cannot be killed while it is on the fish. This stage is very temperature dependent so the ability to get your tank temperature to about 25 o C is important to the treatment of an outbreak. The colder the water, the longer it will take for the
5 condition to progress through its various stages and the longer it will take to treat and eradicate. This is an important reason for my decision to use small square or rectangular fish tanks in our early days. I was able to cover them and, where necessary, easily heat them up to the optimum treatment temperature. This is not so easy with a round 3000-6000 litre tank. Ornamental fish- keepers use a range of chemicals to treat ICH (like Malachite Green) but these are not suitable for use with fish that you are going to eat. Some of my colleagues have successfully treated ICH outbreaks by adding salt to the tank water. This is done in conjunction with raising the water temperature. If you can isolate your growing systems from your fish tank, the time to do it is before you add the salt because your plants are not going to like it. When raising the temperature of the water in your tank, you should increase aeration to compensate for the lower DO levels that are the automatic consequence of warmer water. Moving affected fish is of no use because you will simply transfer the problem to the new tank. Once you detect the symptoms on one or more fish, you should assume that the entire tank is infected and will need to be treated. ICH is one aspect of aquaponics of which (I m delighted to say) I have no direct experience and I intend to do what I can to keep it that way. Preventing ICH (and other fish diseases) is easier than treatment and some useful strategies include: Purchase fish from a source that is clear of the disease. Quarantine all new fish for 21 days. Avoid mixing up fish of different ages. Putting new fish into a tank with your existing fish is simply asking for trouble. Monitor new fish very closely and treat symptoms as soon as they appear. Stress The best disease prevention strategy is to avoid stressing the fish. Some of the more common causes of stress include: Low dissolved oxygen levels Sudden changes in ph or water temperature High concentrations of suspended solids Sub- optimal water temperatures Elevated ammonia or nitrite levels. Handling and/or transporting fish Inadequate diet Stress prevention is simply good management. - o0o-