Freshwater Fish Tank Cycling – how to Prepare for New Fish

Freshwater Fish Tank Cycling – How to Prepare for New Fish

You have probably never seen fish in wild, living in clear, pure water that is free of any contaminants. It’s unlikely. 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 ability of nature to recycle 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? 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. These are the best methods we have found to work based on our experience with hundreds of fish tanks.

Fish-In Cycling

This approach is the most common, used by both beginner and veteran fish keepers alike. Most people cannot watch an empty aquarium for several weeks or months, hoping that beneficial bacteria are actually growing. Here are some tips to get you started.

– When setting up your aquarium, only add a few fish at the start. One small fish is recommended for every 10 gallons. Look at your fish stocking list, and choose the hardiest, most durable species you plan on keeping. – 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. You can also buy live nitrifying bacteria to help 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.

Once you can feed your fish the same amount of food every day for at least a week, ammonia and other nitr levels remain below 0ppm and nitr levels are higher than 0ppm respectively, then the cycle is “complete”. 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. 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. According to Diana Walstad (microbiologist), aquatic plants are more efficient at consuming nitrogen waste than bacteria. A planted tank is a great option! (That said, the leaves and roots of the plants will contribute some beneficial bacteria, but you can add even more using the tips mentioned above.)

Once the plants (or algae) show new growth, the cycle is complete. 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 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. This process is not recommended for beginners. We’ve seen it fail many times and have had to help others in the hobby.

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 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.