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. Most likely 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 Nature’s method of reusing nutrients is called the

nitrogen cycle

. At a very high level, bacteria and plants convert and consume nitrogen compounds from their environment, animals eat the plants and bacteria, and then the plants and bacteria consume the animal’s waste as their 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? Where are the plants and beneficial bacteria that can 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. Look at your fish stocking list, and choose the hardiest, most durable species you plan on keeping. You should start slowly and gradually increase the food intake over the next four to 6 weeks. Although beneficial bacteria feeds off fish waste, it is important to not overfeed your fish until they have enough bacteria to manage their waste. – 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. 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”. (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. All the more reason to go for a planted 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.

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. This process is not recommended for beginners. We’ve seen it fail many times and have had to help others in the hobby.

However, if you’re set on using this method and know what you’re doing, make sure to seed the tank with beneficial bacteria via used filter media or a bacteria additive because otherwise you’re going to 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.