Fishbowl Adviser

Cycling Fish Tank: Everything You Need to Know

Learning about cycling a fish tank can be confusing and overwhelming, having in mind how many articles and videos suggest different tips and methods as the best ones. In our guide, we’ll keep things simple and understandable. Read on to find out everything you need to know about cycling a fish tank.

cory fish in a fish tank

What Does it Mean to Cycle a Fish Tank?

When setting up a fish tank, it’s essential to have beneficial bacteria in the water that will break down toxins and make a safe environment for your fish. The cycling process is exactly that – a process where the good colonies of bacteria remove the toxins (unlike the harmful ones that will make your fish tank cloudy). Ammonia and nitrite have to be converted to nitrate so that they don’t kill your fish since they are highly toxic, even in low concentrations. Still, there’s no room for panic. The nitrogen cycle is a part of every aquarium maintenance, and it’s not hard to understand how it works and how to do it by yourself.

Why Is Cycling a Fish Tank Essential?

The answer is – because you can’t skip the part when the ammonia spikes up and becomes dangerous for the fish. Here’s what actually happens:

  • Nitrogen gets in the aquarium when you feed your fish.
  • They consume the food, and ammonia is excreted. It also comes from decomposed excess food.
  • Nitrosomonas bacteria convert ammonia to nitrite.
  • Nitrobacter bacteria convert nitrite to nitrate.
  • Nitrates aren’t as harmful as nitrite and ammonia, and they are an excellent food for your floating aquarium plants and algae.
  • The level of nitrates also needs to be monitored, which is why we do water changes.

How to Cycle a Fish Tank?

The cycling process happens every day, no matter if you want it or not. If you’re starting a new tank, it’s best that you wait for it to cycle before you add fish, so you don’t risk them getting some sort of disease from the high level of toxins. It’s also not uncommon for fish to die because there’s no established nitrogen cycle and necessary bacteria colonies in the aquarium. So, how to cycle a fish tank? There is a couple of methods you can try

Fish-In Cycle

This method is recommended only if you’re already a professional and you have all the needed experience and equipment. Why is that? Keeping live fish in water that has high levels of ammonia or nitrite can be very dangerous. Also, the levels of ammonia and nitrite should be zero, which is hard to manage if the fish is in the water all the time. The ideal situation for this method would be that you have only one fish for every ten gallons of water. Too many fish only adds up to the level of ammonia, making it harder to reduce and convert.

To do a fish-in cycle, you will need a notebook, pen, and a test kit for ammonia, nitrate, nitrite, and adjusting the pH. It’s the best and safest way to keep track of everything and have a safe environment for your fish. Keep an eye on your pets, see if there are any mood changes, and act accordingly. Make sure you test the water every other day and write down the numbers you get.

Fishless Cycle

Before you add any fish to the tank and start worrying about how to clean a fishbowl, it’s best to leave it to the cycle. It will also help you avoid the NTS or New Tank Syndrome that can be fatal for the fish. How to do a fishless cycle? First, you can take a filter media or some rocks or gravel from a healthy and already established aquarium that has similar parameters as your new tank. Pre-established media will bring the bacteria colonies that you should monitor, and after that, put a few hardy fish to see their behavior. If this is your first tank, and you don’t have anyone to lend you some pre-established media, don’t worry. There are products that you can buy to start the colonies of beneficial bacteria on your own.

aquarium fish

How Long Will This Take?

This depends on the method you chose. What you’re trying to reach is zero ammonia and nitrite level, while nitrates should be below 40 ppm. If you’re doing a fish-in cycle, the process will take between six to eight weeks, while the fishless cycle takes anywhere from four to six weeks. There’s no magical way to speed this up, and you will need patience if you want your pets to have the ideal environment. However, there are some extra tips you can try to save some time:

  • Remove chlorine from the water before adding it to the aquarium to keep as many beneficial bacteria as you can.
  • If your pets allow it, increase the temperature of the water.
  • Don’t ever shut down the water filter.
  • Get an air pump to increase the oxygen level,
  • Test the pH of the water and keep it above 7.


Having anything organic in a closed ecosystem such as the aquarium means that the natural cycles will continue to happen, and everything will still make waste. If you wish for your fish to live a happy and long life, keeping the ammonia and nitrite levels at zero is the first thing you should think about. Learn all about cycling your fish tank and provide your pets the best living conditions.

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