Freshwater Fish Tank Cycling – how to Prepare for New Fish

Freshwater Fish Tank Cycling – How to Prepare for New Fish Do you remember ever seeing a wild fish swimming in crystal-clear water without any other contaminants? Most likely not. It’s not because life is …

Freshwater Fish Tank Cycling – How to Prepare for New Fish

Do you remember ever seeing a wild fish swimming in crystal-clear water without any other contaminants? Most likely not. It’s not because life is sterile. Instead, it thrives in a balanced ecosystem of microorganisms and plants. So, if you’re looking to set up a brand-new fish tank, let’s talk about aquarium cycling and how to prepare a healthy, thriving environment for your fish to live in.


What is the Aquarium Nitrogen Cycle?

The Nature’s method of reusing nutrients is called the

nitrogen cycle

. The bacteria and plants consume nitrogen compounds from their environment at a very high rate. Animals eat the bacteria and plants, and then the bacteria and plants eat the animals’ waste as food.

In an aquarium, the same thing happens. Fish produce waste from eating, which is also known as ammonia. Once the waste has been absorbed by bacteria and plants, the water becomes safer for fish to drink. But wait! What happens if you’ve just set up a new aquarium with tap water, gravel, and decorations? What about the beneficial bacteria and plants that can help to break down the fish waste? That’s why we need aquarium cycling: the process of making sure that your fish tank’s ecosystem can process ammonia without killing any animals.

For more details about how the aquarium nitrogen cycle works, check out our full explanation here.

How to Cycle Your Aquarium

There are several ways to cycle an aquarium, and some are easier than others. Based on our experiences of successfully running hundreds of fish tanks, here are the methods that have worked well for us:

Fish-In Cycling

This is the most popular approach, and it’s used by both novice and experienced fish keepers. Most people cannot watch an empty aquarium for several weeks or months, hoping that beneficial bacteria are actually growing. So, here are a few tips to help you get started on the right foot:

– When setting up your aquarium, only add a few fish at the start. Some people recommend one small fish per 10 gallons. Consider your fish stocking list and decide which species is the hardest to keep. You should start slowly and gradually increase the food intake over the next four to 6 weeks. The beneficial bacteria feeds on fish waste, but since there isn’t a lot of bacteria in the beginning, you don’t want to overfeed the animals until enough bacteria has grown to handle their waste load. – You can significantly speed up the aquarium cycling process by adding beneficial bacteria from the onset. If you already own several aquariums (or have a friend that does), simply transfer some used filter media or substrate from an established fish tank to your new one. To speed up the process, you can buy live nitrifying bacteria.

– Test the water quality with ammonia test strips or multi-test strips. This should be done every other day for the first few days. If you detect ammonia or Nitrite above 0.2ppm, perform a partial water change. This will remove toxic compounds from the water and give your fish clean, new water.

When your fish can eat normal food for one week, ammonia or nitr will be considered complete. Nitr and ate level are both above 0ppm. (At this point, you can begin slowly adding more fish, with some wait time in between – just to ensure the beneficial bacterial growth keeps up with the increased waste load.) While nitrate is safer for fish, it can cause nitrate concentrations exceeding 40ppm. This means that it is time to change the water to reduce the levels.

A water test kit helps you determine if there are toxic levels of nitrogen compounds in the aquarium.

Cycling with Plants

This method is our favorite because it truly transforms your aquarium into a natural ecosystem, both biologically and visually. Rather than setting up a bare tank with very little to no fish, you can immediately add live aquarium plants and then focus on growing them with good lighting, substrate, and fertilizers. In fact, according to microbiologist Diana Walstad, aquatic plants consume nitrogen waste even more effectively than bacteria. This is why you should plant a tank. (The leaves and roots of the plants can contribute some beneficial bacteria. However, you can increase the amount by following the tips provided above.

The cycle ends when the plants or algae show new growth. Your plants are successfully consuming ammonia, nitrates, and converting them to new leaves and roots. Start adding a few fish to your aquarium. Then, use the water test kit and check that ammonia, nitrites, and nitrates, are below 40ppm.

A planted tank not only looks great but also provides better water quality for your fish.

Fish-Less Cycling

This technique for cycling has gained a lot of interest on the Internet, and it involves placing fish food or other source of ammonia in an empty aquarium to grow bacteria. After helping countless people in the hobby, we don’t recommend this process for beginners, since we find that many new fish keepers typically do it wrong and struggle to complete the process.

If you are determined to use this method and you know what to do, you should seed your tank with beneficial bacteria using used filter media or a bacteria additif. Otherwise, you will have a long road ahead.

Final Thoughts about Cycling

Aquarium cycling requires a bit of effort (and patience) on your part, but trust us – the results are totally worth it. By preparing a welcoming ecosystem for your new fish, you greatly minimize loss of life and make your aquarium maintenance routine easier.