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? You probably haven’t. 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 Nature’s method of reusing nutrients is called the

nitrogen cycle

. Bacteria and plants can convert and consume nitrogen compounds in their environment. Animals then eat bacteria and plants. Finally, the bacteria and plants use the animal’s waste to feed their own plants.

In an aquarium, the same thing happens. When you feed your fish, they produce waste (also called ammonia). The toxic waste is then absorbed by bacteria and plants to make your aquarium water more safe for them. Wait! What happens if you’ve just set up a new aquarium with tap water, gravel, and decorations? Where can you find beneficial bacteria and plants to help break down the fish wastes that have been accumulated in your aquarium? 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. We have successfully managed hundreds of fish aquariums and these are our favorite methods.

Fish-In Cycling

This is the most used approach by fish keepers, both new and veteran. 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 recommend 1 small fish per 10gallons of aquarium water. Take a look at your fish stocking and select the most hardy, durable species that you intend to keep. You should start slowly and gradually increase the food intake over the next four to 6 weeks. Beneficial bacteria feeds on fish waste. However, there isn’t much bacteria at the beginning so don’t overfeed them until enough bacteria grows 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. Live nitrifying bacteria can be purchased to speed up the cycle.

– Measure the water quality using ammonia test strips and multi-test strips; this should be done every day or two at first. Do a partial water alteration if you find ammonia (or nitrite) above 0.2 ppm. This will remove any toxic compounds and provide clean water for your fish.

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”. (At this point, slowly adding fish can be done, with some waiting to ensure beneficial bacterial growth is maintained despite the increased amount of waste. 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. All the more reason to go for a planted tank! (The plants’ roots and leaves will provide some beneficial bacteria. But you can do more with the tips provided above.

Once plants (or alga) start to grow, the cycle is completed. 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.

Planting a tank in a garden is beautiful and can improve the 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. We have helped hundreds of people in the hobby. However, we don’t recommend this method for beginners. We find that many fish keepers do it wrong and struggle to complete it.

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 it easier for you to get to the end.

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.