Starting up Your Aquaponics System You ve assembled the components for your AP system and now you want to know how to start and run it. In this section, we cover the most important (and least understood) aspect of operating an aquaponics system...cycling. Cycling Your Tank Do you remember how, during the introduction, we spoke about aquaponics being a symbiotic relationship between fish, plants and bacteria? Well, your goal is to encourage the colonisation of your system with the beneficial bacteria that will effect the conversion of ammonia to nitrates. When your system achieves this state, it is said to be cycling. The bacteria we are seeking are naturally present in the air and water but it will take time to create the concentration of these bacteria that we'll need for nitrification to occur. In ideal circumstances (25 o C and ph 7.5), cycling can occur within two weeks. For practical purposes, you can extend that to 4 6 weeks. In cold weather, and less favourable circumstances, it could take much longer. Nitrogen combines with other elements to form compounds. Some of these compounds become nutrients for some organisms and toxins for others. Ammonia, for example, is required by some bacteria but, at a certain level, it will injure or kill fish. The important thing to understand is that when everything is in balance in an aquaponics system, these organisms all play a role in keeping each other healthy. The fish excrete ammonia which, through the process of nitrification, becomes nitrite and eventually nitrate. By way of a reminder, let s re- visit our earlier discussion on the Nitrogen Cycle. Nitrification is a process where ammonia is exposed to nitrifying bacteria (Nitrosomonas) that convert it to another form of nitrogen called nitrites. Other nitrifying bacteria (Nitrobacter) then convert the nitrites to nitrates. In your aquaponics system, you don t have to know the full intricacies of the Nitrogen Cycle, but you will have to learn how to measure things like ph, ammonia, nitrites and nitrates. You ll also need to know how to interpret the test results and what action to take to ensure that water quality is maintained with appropriate parameters. The reason we cycle a fish tank is to provide an aquatic environment that is non- toxic to the fish that we plan to keep in the tank. In other words, we need to ensure that the nitrifying bacteria that will convert the fish wastes into plant food are in our system in sufficient numbers to cope with the number of fish that we plan to keep in the tank. If we just fill a tank and throw some fish into it, they will produce ammonia through their gills and
2 from their faecal matter. If you just leave them to their own devices, the ammonia and nitrite levels reach a certain point and the fish will become sick and then eventually die. I make no apology if I appear to labouring the point about the importance of cycling a tank correctly. If you fail to understand this aspect of aquaponics, you will be party to the premature demise of many fish. There are two ways you can cycle your system: Live Fish Cycling As the fish produce waste, ammonia is created and, because there are insufficient numbers of nitrifying bacteria present, the ammonia levels will continue to rise to the point where you will have to replace some of the water in the tank to restore the ammonia to within appropriate limits. Within a short time, the ammonia levels begin to rise again, and you replace more water..and so on. You continue this little game of seesaw until eventually the bacteria colonise the tank in sufficient numbers and the tank cycles. This may take weeks or months to occur. In the meantime, if you are not vigilant, you will lose fish. Ammonia and nitrite toxicity need not kill your fish to become problematic. Gill damage arising from the ammonia or nitrites may expose your fish to stress related diseases, or they just may fail to thrive. Some advocates of this method will even suggest leaving the dead fish to rot in the tank to accelerate the nitrogen generation process. Ethical considerations aside, killing fish is a questionable way to cycle a tank. Nitrogen Dosing (Fishless Cycling) Nitrogen dosing (aka fishless cycling) does not rely on the use of live fish and it is my preferred method of starting up a recirculating aquaculture system. Contrary to the advice that you might read elsewhere, don t worry about putting plants into your system initially there s plenty of time for that later. Cycling is largely about setting the system up for nitrification so the initial focus is on the beneficial bacteria. Nitrifying bacteria favour ph in the range of 7.5 7.8, so I d recommend that, if necessary, you dose your water to achieve this level. A nitrogen source (like pure ammonia) is added to the fish tank to encourage the colonisation of the bio- filter by Nitrosomonas bacteria. If you can t locate pure ammonia (don t use any household cleaning product), you can use other nitrogen sources like sulphate of ammonia or urea both of which are available from your local garden store. To cycle a tank, I d suggest that you add the ammonia sulphate or urea at the rate of a teaspoon per thousand litres each day. Begin to test for ammonia.
3 Within two or three days, the ammonia levels in the water will begin to rise. When the test readings reach 2ppm 4ppm, stop adding the ammonia or urea. Once the Nitrosomonas bacteria have begun to convert the ammonia to nitrites, Nitrobacter bacteria will, several days later, begin to colonise the bio- filter, too. Determining when your tank has cycled is easy. When both ammonia and nitrite readings have exceeded 2ppm - 4ppm and then returned to zero your tank has cycled. At this point, you resume adding small quantities of ammonia at regular intervals because, while your system has cycled, it is not necessarily ready to accept a full load of fish. The ongoing addition of small doses of ammonia will provide the feedstock that the bacteria need to continue growing their numbers. This stage of the cycling process will usually only take a few days...while you wait for your fish to arrive. Test your fish tank water daily to confirm that everything is still OK. Prior to the arrival of your fish, adjust your ph levels to 6.5 6.8. You can now plant out your growing system. Caution: Do not overdose your tank with urea (or other ammonia source). The elevated ammonia levels will inhibit the colonisation of Nitrobacter bacteria. Those people who ve experienced difficulty with urea have invariably been too heavy- handed when dosing. I like Nitrogen Dosing because: It s quick and easy cycling times will be reduced (to as little as 14 days) and bacteria colonisation will be more consistent It s decisive..there s no doubt that it has occurred. It saves the water and time associated with water changes. It presents no risk to live fish. Cycling can take from 2 8 weeks (or even longer) depending on a range of factors including nutrient levels, ph, temperature and the means by which beneficial bacteria are encouraged. Cycling a fish tank is only ever an issue with your first one. You can cycle your second and subsequent tanks much faster if you have access to a system that is already operating. You simply cross- connect the two systems and slowly feed the nutrient rich water from the operating system to the new one. This arrangement requires no additional ammonia (it s already coming from the fish in the established system) and the beneficial bacteria will quickly transfer to the new system. The Start Up OK. Now that we understand what has to happen, it s time for the start up. Fill your tank with rainwater or de- chlorinated mains water. Start your pump recirculate water from the tank through the bio- filter and back into the
4 tank again. Add an ammonia source. Undertake daily water tests be patient. When ammonia and nitrite levels spike and then drop to ZERO, your system has cycled. Adjust the ph of the water to 6.5 to 6.8. Add some fish..and then some plants. Introducing Your Fish When introducing fish into your tank, there are two important matters to consider..ph and temperature. If there is too wide a variation in either parameter in the water in the bag containing the fish or the water in the fish tank, you risk stressing or killing the fish. Unless your hatchery delivers your fish in a live tank, it s likely that you will take delivery of them in a plastic bag inside of a styrene box. The bag will have been injected with oxygen prior to its departure from the hatchery. Depending on the duration of the trip, your fish may well have used up most of the oxygen in the bag by the time they arrive, so it s important to get them settled in as quickly as possible. You can place an air stone in the bag to help oxygenate the water. Float the bag on the surface of your fish tank to allow the temperature of the water in the bag to adjust to that of the tank. This will take around 30 minutes. In the meantime, you can check the ph level of the water in the bag (you should already know the ph of your fish tank water) to ensure that there is not too great a variation. Carefully open the bag and over the space of 15 minutes gradually introduce tank water into the bag. The ph levels in the tank and the bag may differ so this gradual mixing may help to avoid stressing the fish. Monitor your fish carefully for the first couple of days after they arrive. Assuming you ve done everything right, they will adjust quickly. We just cover part of the tank with a piece of plywood. This gives the little fish somewhere to escape from direct light while they make the adjustment to their new home. Don't feed your fish immediately after they go into the fish tank...let them settle in. After a few hours, you can feed them small amounts at regular intervals. Suppressing Territorial Behaviour Some species, including sleepy cod, Murray cod and barramundi demonstrate territorial behaviour. They ll harass or attack any other fish if those fish enter their territory. Territorial behaviour can be suppressed by training the fish to live at close quarters from the time that they are weaned. To train 100 fingerlings, confine them in a ventilated plastic crate.of about one cubic foot in
5 size..within a larger tank. Using the ventilated crate forces the fish to be at close quarters with each other while allowing the water to flow freely through the crate. As the fish increase in size, increase the size of the ventilated crate proportionately..until the fish are about 100mm long. They can then be released into the larger fish tank. Some people place hides (lengths of plastic pipe or similar) to give the fish somewhere to hide. These hides encourage territorial behaviour and should not be used. - o0o-