DIY Aquaponics - Bacteria

Bacteria play an important role the health and well being of your aquaponics system by removing the ammonia from the water. This is not a special or magical thing unique to aquaponics, filters in home aquariums as an example use the same families of bacteria to perform the necessary task of removing the ammonia in a very similar fashion.

The Nitrogen Cycle

When our fish excrete waste (we'll call it poo or poop from now on because we're all friends here) the fish poo contains a very high percentage of ammonia. Ammonia in concentrations higher than five parts per million in your tank water is harmfull to fish and in concentrations not much higher than that very toxic and would result in a rapid painfull death. This is not to say that five parts per million is acceptable either, long term exposure would result in your fish dying slowly and painfully instead and they would be more susceptable to disease and illness as well. The ideal amount of ammonia to have in your fish tank is none.

This is where our bacteria come into play. There are two families of bacteria that are beneficial in our aquaponics system just as they are beneficial in an aquarium. The first group is known as nitrosomanas bacteria and they convert the ammonia into nitrites. Nitrite is another harmful toxin that is nearly as dangerous to the fish as ammonia and a second group of bacteria known as nitrobacter are required to convert the nitrite into nitrate. Nitrates are far less harmfull to your fish but once again still toxic above a certain level. Fortunately for us most plants require nitrates to grow and flourish and they will complete the cycle of removing the ammonia from your tank. A healthy, well balanced and established aquaponics system will have less than 0.25 ppm of either ammonia, nitrite or nitrate.

Your aquaponics system growbed is an ideal environment for these bacteria to flourish but it is important to bear in mind that both nitrosomanas and nitrobacter both prefer a growbed that is at least 30cm (1 foot) deep. If your growbed is shallower than this the bacteria will still colonise the growbed but conditions will be less than ideal for them and the aquaponics system may not perform as well as it would otherwise.

Cycling your Aquaponics System

When your aquaponics system is constructed and ready to be used for the first time there will be virtually no beneficial bacteria present, colonies of nitrosomanas and nitrobacter must be established before the system will work correctly. The process of establishing the bacteria colonies in your aquaponics system (or an aquarium for that matter) is referred to as cycling your system.

The nitrosomanas and nitrobacter bacteria are present everywhere around us in the air, in the soil and in water and it is really quite easy to encourage them to inhabit your aquaponics system. When your system is ready to go, there is water in the tank and growing medium in your growbed, but it does not contain any fish or plants introduce a source of ammonia to the tank. Most aquaponic gardeners add a small amount of pure ammonia, fish food or even live fish to the tank. Fish food when it is uneaten and left in the tank will break down and cause the ammonia level to increase. Adding live fish, usually a hardy species such as goldfish, is a dubious approach at best as the fish are at risk as the ammonia level increases and there is also the possibility of disease being transmitted to your food crop fish. One article I read suggested throwing in a handfull of prawns and this is the approach I have taken with great success. I threw in one handfull (about 6 or 7 king prawns) when I commenced cycling and added a second handfull about 10 days later. Once you have added your source of ammonia commence pumping the water from your reservoir through your growbed and back to the reservoir as you intend to do when the system is running.

The amount of time that it takes for your bacteria colonies to become established depends on many variable factors such as water temperature, ambient temperature, the depth of the growbed and many other things besides. In a warm temperate or tropical climate you may have colonies starting to esablish themselves in as little as two to three weeks. It may take substantially longer if conditions are less than optimal.

Bacteria are so small its really difficult to tell if your system has cycled successfully but there is one sure way to tell in the form of an aquarium water test kit. Aquarium water test kits allow you to measure the amount of ammonia, nitrite and nitrate in parts per million and also the pH level of your water. They can be purchased at reasonable cost from aquariums and pet shops and most kits permit hundreds of tests to be performed. I recommend testing every day once you have added your source of ammonia. What you should see is the ammonia levels slowly rise to about 5ppm or so and then drop to zero as the nitrosomanas bacteria become established. Nitrite levels will then start to rise to about 5ppm and then once again drop to zero as the nitrobacter also become established and start producing nitrates.

When you can see the presence of nitrates it is time to add your fish to the tank and plant your vegetables in the growbed. Over the first 6-8 weeks of the systems operation continue to monitor the level of ammonia, nitrite and nitrate within your system. You will find over that time the levels of each will jump around a fair bit and will not be very consistant. This is because the bacteria colonies are still becoming established. If you find ammonia or nitrite levels above 5ppm this can indicate a problem that needs to be addressed immediately or your fish may suffer for it. Nitrate levels can climb to 20ppm without too much issue as long as it doesnt stay there for very long. If you find dangerous levels then it is wise to remove one third of the water from your tank and replace it with clean fresh water. The ideal pH for aquaponics is 6.5-7.0. My system started at 8.0 and slowly dropped without any issues and the fish and plants were not affected.

A Quick Word about Chlorine

Chlorine is often added to tap water to kill bacteria and ensure that it is safe for human consumption. Chlorine is not desirable in aquaponics systems for two reasons, firstly it damages the gills of your fish and kills them and secondly it kills your benefical bacteria too. Chlorine must be removed from your water before adding it to the aquaponics system. Chlorine can be added to drinking water in one of two ways. If it is added as chlorine gas then it will dissipate fairly quickly if you put your water into a bucket or container and allow it to stand for a day or two. If the chlorine is added as chloramine or you would like to use your water immediately there are water conditoners you can buy from pet shops and aquariums that will chemically remove the chlorine for you. If you choose to use a water conditioner or chlorine neutralizer ensure that it is suitable for use with fish intended for human consumption.