Whether you are designing your own system or looking to purchase a prefabricated system you should be aware that it will take some time for your system to function so that fish and plants are both healthy and growing. The process of establishing this symbiotic relationship is referred to as "cycling".
You can cycle with fish or without fish. The choice is yours. Whether you cycle with fish or without fish, you will need to keep an eye on the water chemistry so go ahead and invest in a good water quality test kit. These kits will allow you to test for pH, ammonia, nitrites, and nitrates.
I have cycled systems both ways and I prefer fishless cycling. I will admit it: I am a mushmellow. It bothers me when fish die. I feel like I am their steward and when they die I have failed them. The truth is when you cycle with fish some fish are going to die. During cycling there will be ammonia and nitrite spikes that will kill fish. It is a natural part of establishing the system. Even if they are just the cheap little feeder goldfish from the pet store, it hurts me when they die. So I like to cycle without the fish.
In fishless cycling you add ammonia to the fish holding tank (that has no fish in it) in an amount sufficient to bring it up to 0.5 ppm. You then test the water daily until levels fall back below 0.5. You add ammonia again to bring it up to 0.5 and wait for it to drop. After a week or two of this you will start to see some nitrites show up. These are the nitrosomona bacteria that are establishing themselves in the system and will start to convert that ammonia to nitrites. You should see a big spike in nitrites before the nitrates show up. Once the nitrates show up that means you have nitro bacters growing in the system. These guys will take nitrite and convert it into nitrate. Once this cycle is established you can safely add fish to the system.
The amount of time it takes to cycle a system without fish can vary from 3 to 6 weeks. Things that affect the cycle time period are water temperature and pH. Keep your water temperatures on the warm side and the pH in the neutral zone. Also, if you start cycling with water straight from the tap, it will have chlorine in it. This chlorine is there to kill the unsafe bacteria in your drinking water. It will also kill your nitrifying bacteria. That means anytime you use straight tap water you are setting yourself back. Luckily chlorine readily off-gasses and if you let your water stand for 24 hours the chlorine/chloramine will dissipate and you can safely use it in your aquaponic system. This is especially true when you need to top off an existing system.
Cycling takes patience. In the mean time, enjoy the plants that you put in your system. You have to have plants for the cycle to be established, so plant some water loving plants. Things like basil, mint, and tomato will do well in a system that is not cycled. This is because they like water and the lack of nitrogen doesnt really bother them. In fact, if nitrogen levels get too high, tomato plants will grow but not bloom! Onions are also great plants for cycling. Ive even cycled with petunias!
There is another method of fishless cycling that is mostly promoted by men. It is called "pee-ponics" and instead of adding pure ammonia from the store into the system, human urine (referred to as "hummonia") is added to the system. Dont really understand why men want to pee into their aquaponic systems, but to each their own.
You can speed up cycling by inoculating your system with bacteria from a healthy system that is already established. This can be done by taking water from the filter of a healthy system or simply taking water from a healthy system. Be very careful when doing this. If the system from which you take your water is not healthy, then you have just spread its disease to your system. If you have one already cycled and well operating aquaponic system, then by all means harvest the bacteria from your existing system to jump-start your new system.
Lastly, you can go to a pet store that deals in aquariums and purchase bacteria in a bottle. I am not a fan of this because it is pricey and honestly, how long can those bacteria live in a bottle?
How do you cycle? Id love to hear your experiences.
