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How to Cycle a Fish Tank: The Beginner’s Guide

When setting up a fish tank for the very first time, there are a few tasks that can feel rather daunting to an absolute beginner, and cycling a new fish tank is undoubtedly one of them. Vital to the health and wellbeing of your new finned friends, your ability to safely guide them through the aquarium cycle is your first test in creating a happy, comfortable home for them to spend their days. Fortunately, if this is your first time setting up an aquarium and you don’t know how to cycle a fish tank, the experts here at Aquacadabra are ready to take you through the process step-by-step.

What is cycling a fish tank?

If you’re unfamiliar with the tank cycling process and don’t know exactly what it is or why it’s important, then you wouldn’t be the first. Put into the simplest terms, cycling a fish tank is the method by which you ensure that the water in your aquarium is a safe environment for your fish, snails, crabs, plants, coral and more to live. This is done by encouraging new, healthy bacteria to grow in your tank, which will have the job of ensuring that your water goes through the nitrogen cycle without endangering your livestock.

Once this initial aquarium cycle has been completed (with your careful help and encouragement) you can then leave your tank to safely cycle on its own, with those brand new bacteria colonies working hard to keep your tank safe without constant monitoring from you.

What are the 3 stages of the nitrogen cycle in a fish tank?

The nitrogen cycle, while a little intimidating to influence in your own tank, is very simple to understand. Learn each of the three stages of the nitrogen cycle below:

  1. Step one in the nitrogen cycle is the production of ammonia. This chemical occurs naturally through the decomposition of fish waste, which breaks down in the water, and is toxic to the fish who created it. Usually, you can expect ammonia levels to rise after around three days of introducing livestock to a new, uncycled aquarium.
  2. Step two of the nitrogen cycle is the conversion of ammonia into nitrites. This stage occurs by the first type of important fish tank bacteria: nitrosomonas. These handy nitrite-forming bacteria convert the high levels of toxic ammonia in the water into nitrites. Unfortunately, nitrites are also toxic to fish in high quantities, but this chemical compound must occur before your fish tank cycle can move onto the next phase.
  3. The last stage of the nitrogen cycle in a fish tank is the production of nitrates. This process occurs through the development of nitrate-forming bacteria, called nitrobacter, which work to convert toxic nitrites into nitrates. While nitrates are significantly less toxic than ammonia and nitrites, they still pose a threat to your fish when produced in high levels, but this is easily counteracted through your regular ongoing maintenance tasks.
nitrogen cycle

How to cycle a fish tank: Step-by-step guide

If this is the first time you’re hearing about the nitrogen cycle in your fish tank, you might be a little intimidated by the mention of toxic chemicals - but you don’t need to worry too much. Cycling a new fish tank is undoubtedly important and requires some effort, but is definitely a manageable task for a beginner fishkeeper. To help take you through the process, we’ve created an easy-to-follow, 5-step guide to tank cycling for you to work through:

Step 1: Set up your tank

Before you can start cycling your tank, you’ll first need to set up your new aquarium. This will include all of the essentials (substrate, lighting system, filter and heater if applicable), as well as your water. It’s also important to make sure that you’re filling your tank with dechlorinated water, as chemicals such as chlorine and chloramine, which are commonly added to tap water for their antibacterial properties, will interfere with the healthy growth of nitrosomonas and nitrobacter bacteria. If you haven’t already, buying a water conditioner, such as the Seachem Prime or Tetra Aquasafe, is recommended to ensure clean water for initial filling and all future water changes.

Once everything has been set up and the equipment turned on, we would recommend leaving the new aquarium to run for around one week before moving onto the next step. During this time, it would also be a good idea to add a filter starter to the system. Bacteria boosters such as Fluval Cycle and ATM Colony help to introduce essential nitrifying bacteria to the filtration system instantly, giving them the headstart they need to grow within days instead of weeks.

Step 2: Introduce livestock

The nitrogen cycle in a fish tank can’t start without that crucial first ingredient: ammonia. And, as ammonia is created through the decomposition of fish waste, you’ll first need to add some fish. Of course, with ammonia being toxic to fish, taking some precautions before the first cycle is a smart move, and we would recommend these two methods. First, start small with just a few fish as this will keep the level of fish waste, and therefore ammonia, to low levels. Second, choose hardy fish for cycling such as tetras and danios, which are more likely to withstand the harsh environments created by the first nitrogen cycle.

Step 3: Limit ammonia production

If you’ve decided to take our advice and only add a small number of fish into your new tank during its first aquarium cycle, then you’ll already have taken the first precaution against the over-production of ammonia. The next piece of advice we can give is to be careful during your feeding time for those fish. Make sure that you don’t overfeed them as they’ll naturally produce more waste, and any uneaten food will also decompose, making matters worse (by producing even more ammonia).

Step 4: Reduce pollutant levels

Once you’ve created the conditions for the nitrogen cycle to start in your new fish tank, it will occur without any extra encouragement from you. From now on, your job is to make sure that your fish survive the process by keeping the ammonia and nitrite levels to a manageable level. This involves changing between 10%-25% of the water in your tank every few days with clean, dechlorinated water to dilute the amount of pollutants in your tank.

Step 5: Monitor cycle progress

Provided you’re staying on top of keeping your cycling tank safe for your hardy livestock, your only remaining job is to keep track of the progress of the nitrogen cycle with a water test kit. Not only can a test kit determine which phase of the nitrogen cycle your aquarium is in, but it can also measure the concentration of ammonia and nitrites in your water, helping you to ensure they’re kept within survivable levels for your fish.

There are a wide range of test kits available at Aquacadabra, including individual ammonia, nitrite and nitrate tests and water test kit sets. Which type of test you want depends on your personal preferences and budget, and you can see a few of our top recommendations below.

How can you test the ammonia, nitrite and nitrate levels in your fish tank?

Individual test kits

While we would recommend investing in an all-in-one water test kit due to its benefits for ongoing maintenance, if you prefer to start with only the essentials, we have individual test kits available which cover each of the three chemicals vital to an aquarium cycle. NT LABS is one trusted brand we have at Aquacadabra, who produce trustworthy and easy to use ammonia, nitrite and nitrate tests for your aquarium.

Manual test kits

If you’re committed to conducting regular manual tests to ensure the quality of your aquarium water from the cycle and beyond, investing in a combination test kit set is worthwhile. There are plenty of excellent kits to be found in the collection at Aquacadabra, but we recommend the JBL Test Combi Set plus NH4 kit in particular. Covering a range of water parameter tests, including the cycle essentials of ammonia (NH4), nitrite (NO2) and nitrate (NO4), you’ll know exactly what’s happening in your water.

Cycling a fish tank FAQs

There you have it: our complete beginners guide to cycling a fish tank. By now, you should hopefully know what the nitrogen cycle is as well as how to make sure it's completed safely in your own new aquarium. Of course, this won’t make you an expert in all things tank cycling, but we’ve put together a few extra pointers below in case you still have any questions.

Will my fish die if I don't cycle the tank?

Unfortunately, yes. Fish who are introduced to a tank will immediately start producing natural waste which will, inevitably, decompose and turn into ammonia. This is the first step in the nitrogen cycle of a fish tank but, without assistance, these highly harmful ammonia levels will build up and pose a serious threat to your aquarium livestock.

What is new tank syndrome?

If a tank has ‘new tank syndrome’, it has fallen prey to the dangers associated with the first nitrogen cycle and has become saturated with toxic chemicals. Unfortunately, the true danger of new tank syndrome is the effect it can have on any livestock in the aquarium. Unable to stand up to the harsh conditions, fish who live in the ammonia and nitrite rich environment of a tank with new tank syndrome are in serious danger of experiencing illnesses and even death.

As we’ve mentioned, some species of fish have a stronger resistance to living in ammonia and nitrite rich water, though none are immune, so a good idea is to stock your tank with hardy fish for cycling. Such fish include danios, guppies, barbs, minnows and tetras, but if you have your heart set on a specific species for your new aquarium, it’s worthwhile discussing how well they stand up against tank cycling with your local seller. If they wouldn’t recommend them as a hardy fish for cycling, an alternative approach could be to cycle the tank with a few minnows before introducing your more delicate fish further down the line.

How long does it take to cycle a fish tank?

While the steps we’ve detailed in this blog can usually be completed within a 6-8 week period, there’s really no telling how long it will take to cycle a fish tank. There are too many variables to consider, from the size of the tank to the number of fish residing in it, so there is no definitive way to put a time scale on such a project. Instead, the only advice we can offer is to be patient and prioritise the health of your fish over any timeline. Once the cycle has been completed, the hard work and effort you’ve put in will start to pay off, and your maintenance duties will be reduced significantly.

Does temperature affect tank cycling?

Yes, water temperature has a direct impact on a cycling tank. This is because the ultimate goal of cycling a tank for the first time is to grow important nitrifying bacteria, and the temperature needs to be conducive to bacterial growth for this to happen. The best temperature for this is typically between 25-30°C (77-86°F), but this must be balanced with the needs of your chosen livestock. Minnows, for example, need an environment that is kept between 18–22°C (64-72°F), and so couldn’t be kept at such high temperatures. Instead, we would recommend prioritising the temperature your fish need to live and selecting fish which prefer a temperature of at least 18°C as bacterial growth will be significantly diminished in environments colder than this.

How can I cycle my fish tank faster?

If 6-8 weeks sounds too long, there are a few methods you can try to speed up the process. Though we would typically advise beginners to take their time, if you’re determined to quicken your first aquarium cycle, these are our safest recommendations:

  • Grow aquarium plants

Introducing living plants to your aquarium before you add livestock to begin the nitrogen cycle is a good way to speed up the process. This is because aquarium plants use ammonia, nitrite and nitrate as they grow, helping to reduce toxicity levels naturally and maintain a healthy balance in your aquarium. On top of this, plants also carry their own beneficial bacterias which can help to break down ammonia faster than using a biological filter system alone. Of course, caring for aquatic plants brings its own unique challenges down the line (such as pesky plant-eating fish dining on all your hard work), but they are undeniably a beautiful inclusion to have in any fish tank.

  • Increase oxygen levels

One factor that has an impact on the growth speed of nitrifying bacteria is oxygen level. If your tank water is under-oxygenated, both your fish and your bacteria will suffer. In order to increase oxygen levels in your cycling tank, we recommend investing in an oxygen air pump, such as the Eheim Air Pump 400 or TetraTec APS50 Air Pump. This will create a steady and controllable flow of bubbles, helping to boost oxygen levels during your first aquarium cycle and beyond.

  • Use old filter media

As the speed of the aquarium cycle depends on the growth of beneficial bacteria in your tank, one of the easiest ways to shorten the time it takes to complete the first cycle is to introduce live bacteria to your tank right away. A classic tactic shared by experienced fishkeepers is to take filter media from an established aquarium and add it to your new tank. This media will already have a living colony of useful nitrifying bacteria which can jumpstart the cycle in your new fish tank.

  • Use a bacteria booster

Unlike the second tactic for cycling a tank, which relies on access to filter media from an established aquarium, anyone can use a bacteria booster. Available at Aquacadabra, products such as Fluval Cycle and ATM Colony contain commercial grade nitrifying bacteria which can be safely added to a brand new tank to establish a bio-filtration system quickly.

  • Consider fishless cycling

Throughout this guide, our advice and instructions have detailed how to cycle a tank with fish. The most common way to cycle a new tank, the fish-in method can take a long time even when additional quickening techniques are used such as the addition of plants and nitrifying bacteria colonies. Fortunately, if you’re on a tight schedule, or simply don’t want to risk subjecting your fish to a tank with new tank syndrome, there is another method you can try: fishless cycling.

What is fishless cycling?

As the name suggests, fishless cycling is the process of cycling a fish tank without fish. There are a number of benefits to this method which make it a good choice for beginners and experienced fishkeepers alike, the biggest one being the significant reduction of risk to fish. Fishless cycling ensures that your finned friends and other aquatic livestock are kept away from the toxic chemicals of a tanks first nitrogen cycle, meaning they can be introduced to a less hostile environment later on.

The other significant benefit of fishless cycling is that it takes significantly less time to complete than cycling with fish, taking as little as 8-12 days, depending on your method. This means that you can get your brand new tank up and running quickly and safely in a matter of weeks.

How do you start a fishless cycle?

If you’re considering using the fishless cycling method on your new tank, make sure you do so safely by following our step-by-step instructions.

Step 1: Set up your tank

Just as you would if you were starting the tank cycle using the fish-in method, the first step in fishless cycling is to set up the aquarium. Once again, this will require all of your essential equipment, dechlorinated water and one week of running the aquarium without any interference.

Step 2: Introduce ammonia

After a week of running all of the aquarium equipment, your next task in completing the fishless cycle is to add ammonia. Of course, without fish to produce ammonia through waste, the only option is to introduce the chemical manually. When searching for where to get ammonia for your aquarium, make sure to avoid ammonia solutions such as those you would use for cleaning and instead, choose an aquarium-specific solution, such as Dr Tim’s Ammonium Chloride Solution. Made up of reagent-grade materials, this pure ammonia solution can be added to your aquarium in drops to start the cycle, but the amount you need to add will change depending on the volume of water in your tank. Follow the concentration instructions on your chosen product, using your water test kits to ensure the system isn’t overdosed. As a guide, ammonia concentration in fishless cycling should be kept between 2-3 mg/L, and should not exceed 5 mg/L.

Step 3: Maintain ammonia concentration

Once you’ve added your ammonia solution, your next step should be to leave the tank to cycle without interference for 2-3 days. After this settling period has passed, you’ll need to use your test kits to measure the levels of ammonia and nitrites in the water every 2-3 days, which will allow you to track the appearance of nitrite. Once this chemical begins to appear, you will know that beneficial nitrosomonas bacteria has begun to grow and you can once again increase the ammonia levels (how much you add will once again depend on the product you’ve chosen, but if you’ve opted for our recommended Dr Tim’s Ammonium Chloride Solution, add half of the initial dose).

After this second dosage, continue to monitor the ammonia and nitrite levels every 2-3 days until ammonia levels fall between 0-1 mg/L and nitrite continues to be present. Due to the speed at which ammonia is converted into nitrite, you shouldn’t expect to see any spikes in nitrite until after 2-3 weeks of starting the fishless cycle, but keep monitoring with the regular testing regime all the same. Simultaneously, you should continue adding ammonia at the same intervals, lessening the dose to a quarter of the initial dose to avoid the overproduction of nitrite.

Before long, your water tests should show a drop in the level of nitrite in the water. It is natural for this to occur very suddenly, converting into the final product: nitrate. Once this happens, the last test you’ll need to perform to ensure the fishless cycle has been successful is to add one final, full-sized dose of ammonia to raise the concentration back to 2-3 mg/L. You will know that it’s time to start thinking about adding your fish when this dose is converted overnight from ammonia, to nitrite, to nitrate, the test showing no nitrate present in the water.

Alternative step 3: Use DrTim’s Aquatics One & Only Live Bacteria

As you may have noticed, the fishless cycling technique can take just as much time and effort as the fish-in method. The only way to bypass this is to invest in DrTim’s Aquatics other miraculous fish cycling product, the One & Only Live Nitrifying Bacteria. Capable of speeding up the process considerably, this addition can see a fishless cycle be completed in as little as a week. If this is your preferred method, simply follow the steps 1 and 2 as detailed above, before completing the following tasks.

To recap, on Day 1 you should first add the correct dosage of ammonia solution to your new aquarium and ensure that the concentration measures around 2 mg/L, then you can immediately add your One & Only bacteria (note that, unlike ammonia, you can’t overdose your tank with this product, so there’s no need to be concerned). Once this has been added, you should wait until Day 2 before measuring both the ammonia and nitrite levels in your tank.

On Day 3, test your water again and, if you find that the ammonia and nitrite levels have fallen below 1 ppm, you can add another full dose of ammonia (note that, with the addition of One & Only already in the tank, you can no longer use an ammonia test to take this to 2 ppm again, instead simply add the full dose). With this added, continue your daily testing schedule.

Before long, usually between Days 5 or 6, you should see your levels return to below 1 ppm for both ammonia and nitrite. Administer another dose of 2 ppm ammonia solution and continue your daily testing. The goal of this is to continue growing the bacteria colony so that it can convert ammonia into nitrite, then into nitrate quickly, constantly keeping the toxicity of the water at a minimum for your livestock once they’re added.

As soon as you see your ammonia and nitrite levels both reach below 0.2 ppm, add another full dose of ammonia and continue your daily measurements. Continue this process of adding a full dose of ammonia each time both ammonia and nitrite concentrations reach 0.2 ppm until this level is reached within a day of the dose being administered. Once this occurs, your tank has enough healthy nitrifying bacteria to be considered successfully cycled!

Master the fish tank cycle at Aquacadabra

Ready to complete your first aquarium cycle? Whether you’re brand new to the challenge of creating a vibrant tank filled with exciting aquarium life, or just needed a quick refresher course before embarking on a new fishkeeping adventure, you’ll find everything you need to master the fish tank cycle at Aquacadabra. From a wide range of water test kits available online to helpful advice from our fishkeeping experts, your new tank couldn’t be in safer hands.

Once you’ve successfully made it through your first tank cycle, you can also find effective and reliable ammonia measurement products online at Aquacadabra to ensure the safety of your fish for years to come. From the affordable Seachem Ammonia Alert to the more advanced Seneye USB Home V2, these helpful monitors will alert you to the appearance of dangerous increases of ammonia in your cycled aquarium, prompting you to take action before it's too late.