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? 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?

Nature’s way of recycling nutrients is known as 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. Your fish produce waste when you feed them. Then bacteria and plants absorb this waste to make the water safer for your fish. 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. Here are our top picks based on hundreds of fish tank runs.

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. 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. Take a look at your fish stocking and select the most hardy, durable species that you intend to keep. Start slowly with your fish and increase gradually over the next four to six week. 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. 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. Whenever you see a detectable amount of ammonia or nitrite (anything above 0.2 ppm), do a partial water change to remove the toxic compounds and provide new, clean water for your fish.

– 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. At this point you can slowly add more fish to the tank, with some time between each addition – in order to maintain the beneficial bacterial growth and reduce the 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. According to Diana Walstad (microbiologist), aquatic plants are more efficient at consuming nitrogen waste than bacteria. This is why you should plant a tank. You can also add beneficial bacteria to the roots and leaves of your plants by using the tips above.

The cycle ends when the plants or algae show new growth. Your plants are successfully consuming ammonia and nitrates and converting them into 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. This process is not recommended for beginners. We’ve seen it fail many times and have had to help others in the hobby.

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 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.