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. This is because life doesn’t thrive in “pristine” environments. It flourishes when there are a variety of plants and microorganisms that interact with each other. 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

. 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. 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 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. (Some people recommend 1 small fish for every 10 gallons of tank water.) Look at your fish stocking list, and choose the hardiest, most durable species you plan on keeping. Start slowly with your fish and increase gradually over the next four to six week. 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. You can also buy live nitrifying bacteria to help 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. 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. 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. Nitrate is a safer compound for fish, but once it rises to concentrations more than 40 ppm, you know it’s time to do a water change to lower the nitrate 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. Microbiologist Diana Walstad says that aquatic plants actually consume nitrogen waste more efficiently 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 is complete when the plants (or alga) 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 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.

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.