Aquarium Cycling – The Complete Guide to Cycling a Fish Tank

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Cycling an aquarium is the most important thing that you will ever do to ensure the long term health of your fish, yet few people who are starting out with new aquariums have ever heard of it. And the consequences of not cycling an aquarium can be dire, and often results in tank full of dead fish – which is usually followed by people giving up on keeping fish in frustration.

So to start with, what is cycling? To put it as simply as possibly, cycling an aquarium is the act of building up beneficial bacteria in an aquarium, that break down the fishes waste. Some people may remember the nitrogen cycle from high school science class, and this is a limited version of that occurring in the tank.

Through cycling, bacteria that will break down ammonia and nitrates are slowly established in the tank. And when I say slowly, I mean very slowly. Most people are used to the idea of hordes of bacteria multiplying almost overnight, but the bacteria that process ammonia and nitrates take weeks to grow. So it needs to be closely monitored to see where you are in the cycle.

Once you have properly cycled a tank, any fish that are added to the tank won’t die the first time they tank a poop. The bacteria that you have helped to establish, will first break down the waste into ammonia, then into nitrites, and finally into nitrates which are then removed during weekly water changes.

Cycling with Fish

For many years, using a few sacrificial fish was the most common way to cycle an aquarium. Nowadays most people view this method as cruel, but it is still probably the most popular way to cycle an aquarium. One of the major selling points, is that it provides some action in the tank – instead of just watching an empty tank for weeks on end.

To start the process of cycling an aquarium with fish, you first need to add a handful of small, very hardy fish. The most common fish to use are zebra danios, and these little fish can often cycle an aquarium with few ill effects.

Once the fish have been added to an aquarium, their waste will begin to break down into ammonia, and feed the few the bacteria that exist in the tank that feed on ammonia. These bacteria will start to multiply and will break down the ammonia into nitrites.

The process then repeats itself, as bacteria that feed on nitrites start to reproduce, and break the nitrites down into nitrates. The nitrates can then only be removed through the addition of live plants or through water changes.

The reason that cycling an aquarium with plants is generally frowned upon is that ammonia and nitrites are deadly to fish. Any fish that are present as the bacteria build up to break these down can suffer immensely, and will likely end up with reduced life spans.

Fishless Cycling

The more modern method for cycling aquariums is the fishless cycle. This process is often considered boring by many new aquarists who want nothing more than to add fish to their tank, but is far more humane to the fish. Instead of adding fish to the tank, and allowing their waste to start the cycle, another source of ammonia is added to the tank.

To start with, pure ammonia, or an acceptable alternative is added to a newly set up aquarium. If you can’t get your hands on ammonia, you can add a large quantity of fish food, or some people have reported success by adding a shrimp to the tank (not the living kind).

The source of ammonia will start to feed the bacteria in the tank, and they will begin to multiply and break down the ammonia in nitrites. The population of the bacteria that feed on nitrites will then begin to grow and begin to convert the nitrites into nitrates.

Most people will check the progress of the cycling with regular tests – first for ammonia, then nitrites and finally nitrates. This will help to ensure that the process is progressing properly, and will help you identify any issues.

To ensure that the process has been completed successfully, you will have to test it at the end. If it was done properly, you should have levels of ammonia and nitrites that both read 0 ppm, and nitrate levels that are under 20 ppm.

If you are set on cycling an aquarium with fish, you should at least consider adding plants. Plants will significantly speed up the cycling process, and will use both ammonia and nitrites at fertilizer. This helps to lower the levels of ammonia and nitrites in the water, which will be greatly beneficial to the fish.

When choosing plants to use, you should only select fast growing plants like Hornwort, Anacharis, Water sprite and Water Wisteria. While slower growing plants can be added later, they should be avoided since they won’t be able to keep up with the levels of ammonia and nitrites.

Jump-starting Cycling

There are several ways that you can jump-start a cycle, and speed up the process. Unfortunately, all of these methods require access to an existing, established aquarium so they may be difficult to come by for someone first setting up an aquarium.

Gravel – The gravel from an existing tank will already have all of the beneficial bacteria present on its surface. This can be added to a new tank, and the bacteria from the gravel will quickly colonize the rest of the aquarium. This can cut the amount of time needed to cycle a tank, and is the method most often used among aquarists to help cycle a new tank.

Filter Media – No place in an aquarium contains more beneficial bacteria than the filter media, and a small piece can be removed and placed in a new aquariums filter to quickly colonize it. This method, while slightly less popular than gravel, is still very effect

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