Freshwater Fish Tank Cycling – how to Prepare for New Fish


Freshwater Fish Tank Cycling – How to Prepare for New Fish

Have you ever seen a fish in the wild living in pure, crystal clear water with no other contaminants? Probably not. That’s because life isn’t sterile; it doesn’t flourish in “pristine” conditions, but rather when there’s a whole ecosystem of microorganisms, plants, and animals that are in balance with one another. 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 ability of nature to recycle nutrients is called the

nitrogen cycle

. Plants and bacteria convert nitrogen compounds to plants at an extremely high level. The animals then eat the bacteria and the plants then eat the bacteria’s 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. Wait! What happens if you’ve just set up a new aquarium with tap water, gravel, and decorations? Are there beneficial bacteria and plants that could help you break down the fish wastes? 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. Here are our top picks based on hundreds of fish tank runs.

Fish-In Cycling

This method is most commonly used by 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. One small fish is recommended for every 10 gallons. Take a look at your fish stocking and select the most hardy, durable species that you intend to keep. – Feed your fish very lightly at first and then gradually increase the amount over the next four to six weeks. Beneficial bacteria feeds on fish waste. However, there isn’t much bacteria at the beginning so don’t overfeed them until there is enough. – 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. Live nitrifying bacteria can be purchased to speed up the cycle.

– Use ammonia and multi-test strips to measure the water quality. It should be done once or twice daily at first. 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.

– The cycle is considered “complete” once you are able to feed your fish normal amounts of food for a week, and ammonia and nitrite levels stay at 0 ppm while nitrate levels are above 0 ppm. You can add fish slowly, but with some waiting time – to make sure the beneficial bacteria growth continues to grow despite the increased waste load. Although nitrate is considered safer for fish than other compounds, it should be removed from the water supply once it reaches 40 ppm.

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. All the more reason to go for a planted tank! You can also add beneficial bacteria to the roots and leaves of your plants by using the tips above.

The cycle is complete when the plants (or alga) show new growth. Your plants are successfully converting ammonia and other nitrates into new roots and leaves. 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 is not only beautiful to behold but also improves 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.

You can use this method if you want to and are confident in your knowledge. However, it is important to ensure that the tank is sown with beneficial bacteria by using filter media or adding a bacteria additive. This will make your journey easier.

Final Thoughts on 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.