How to Do a Fishless Cycle in Your Aquarium

What is a Fishless Aquarium Cycle?

Starting an aquarium is an exciting journey, but every new tank needs to first go through an important step before you can safely add fish: the nitrogen cycle. In simple terms, this process is about building up beneficial bacteria in your tank that will help to break down toxic substances like ammonia and nitrite, which will make the water safe for fish to live in.

Traditionally, people used to start this process with fish in the tank. But, that method can harmful to the fish as they are exposed to high levels of ammonia and nitrite during the cycling process. That’s where the fishless aquarium cycle comes in. It’s a way to prepare your tank without risking the health of any fish. Instead of relying on fish to produce waste (to start the cycle off), you use pure ammonia (ammonium chloride) to feed the bacteria, allowing them to develop without putting any fish at risk.

By choosing the fishless route, you’re creating a healthier environment for your future fish and ensuring that when you finally do add new fish, they can settle into a stable, safe home. Plus, it will teach you the basics of water chemistry, and how fast your tank can clear any ammonia spikes, helping prepare you for any future water issues you might run into!

Why Choose a Fishless Cycle for Your Aquarium?

If you’re new to the aquarium hobby, you might wonder why fishless tank cycling is recommended. After all, it means you will need to wait before you can see newly added fish swimming around in your aquarium. So, it might sound like an extra step, but it actually offers some major advantages and can result in a faster cycle time.

The biggest reason is simple: no stress for the fish. The spikes in ammonia and nitrite that occur during a traditional cycle can be very stressful, if not fatal, for them. It can damage and burn the fish, particularly their gills, meaning that even if the fish do survive the process, they may not live as long. Whereas, fishless tank cycling skips that risk entirely. Instead, you regularly add a controlled amount of ammonia to the tank yourself, allowing the beneficial bacteria to grow without needing any living creatures in the tank to produce the ammonia at all. This makes for a much smoother transition when you finally introduce your fish.

Another perk? It’s faster and more efficient. Without fish, you can add higher levels of ammonia, which speeds up the growth of the bacteria that you need. This means your tank can cycle more quickly, getting you closer to that exciting moment when you can add your fish.

In contrast, if you were to cycle your tank with fish in it, you would need to do frequent water changes throughout the process (to keep the toxicity levels low enouhg for the fish to survive). This all takes time, both for the water changes and because you will also remove some bacteria and ammonia each time. Thus, slowing the build up of those all of those important beneficial bacteria. Another consequence of this, as you will have cycled your aquarium for a lower concentration of ammonia, you wont be able to add as many fish in at the beginning as you would if you were to do a goals cycle. This is because there will not be enough bacteria to keep up with the rate of ammonia production.

Overall, choosing a fishless cycle is about creating a safer, more balanced environment. It requires a little extra patience up front before you see a fish in your tank, but your fish will thank you for it and so will your future self for creating far less work for yourself in the long run!

What Do You Need for a Fishless Cycle in Your Aquarium?

Getting started with a fishless cycle is pretty straightforward. You’ll only need a few key items on hand to make sure the process goes smoothly:

1. Aquarium and Equipment:

– Of course, you’ll need your tank! Make sure it’s set up with a filter, heater (if you’re planning on keeping tropical fish – warmer water also speeds up the process), and a light. An aquarium filter is essential since the filter media is where a lot of the beneficial bacteria will live. We have a post that covers essential aquarium accessories and equipment when setting up your tank, if you want to read more details on this section.

2. Pure Ammonia (aka Ammonium Chloride):

– This is the magic ingredient when it comes to a fishless cycle. You can usually find pure ammonia in hardware stores or online. Just make sure has no other additives such as added scents, dyes, or surfactants (these can harm your tank). Ammonia is what kickstarts the whole process, simulating fish waste and feeding the beneficial bacteria. My favourite go to for this is Dr Tim’s, however, any source of household ammonia and brand will do as long as it’s pure. Just make sure to make a note of the percentage concentration so that you can work out the correct dosage.

3. Water Test Kit:

– A reliable water test kit is your best friend during the cycling process. You’ll need it to monitor the ammonia, nitrite, and nitrate levels throughout the cycle. Liquid test kits are typically more accurate than test strips, so they’re worth the investment. My go to for this is the API master test kit – which you can normally pick up for a petty good price on Amazon.

4. Dechlorinator (Water Conditioner):

– If you’re using tap water, it likely contains chlorine or chloramine, which will kill off beneficial bacteria. A dechlorinator will neutralise these chemicals and make your water safe for cycling. my favourite water conditioner is Seachem Prime – for a number of reasons that I won’t go into here. Yes, I know it can seemsexpensive gram to gram with other brands, but it does a whole heap more and you only need to use a fraction of the amount each time, so it ends up lasting a lot longer too.

5. Patience:

– Okay, you can’t exactly buy this one, but it is important here! Fishless cycling takes a few weeks, and there may be times when it seems like nothing is happening. Stick with it, keep testing, and know that every day brings you closer to a fully cycled tank.

To help with this, I recommend keeping a daily diary of the process. Note down your dosing amount, as well as ammonia readings, nitrite readings and nitrate readings. That way you’ll see that things really are happening (even when it doesn’t feel like it), and you’ll also get familiar with the regular dosing amount needed, as well as how quickly your tank can clear ammonia spikes.

Once you have these essentials on hand, you’re ready to dive into the actual cycling process.

Step-by-Step Guide to a Fishless Aquarium Cycle

Cycling your aquarium without fish might seem complicated, but it’s quite manageable if you follow these steps:

Step 1: Prepare Your Tank

– Set up your aquarium with the filter, heater, and any tank decorations, and fill it with dechlorinated water. Make sure the filter is running properly and that the water temperature is stable, especially if you plan on adding tropical fish later. This creates an environment to keep your beneficial bacteria healthy as they grow.

Step 2: Add Liquid Ammonia (Ammonium Chloride)

– Add your source of pure ammonia to the fish tank to simulate fish waste. A common starting point to aim for is around ~3ppm (parts per million) of ammonia. Aim to always keep it below 5ppm, wherever possible, throughout the whole process. Check below to see a rough guide on how to calculate the dosage.

How much ammonia should you use? Below is a rough guide to achieve 3ppm in your tank. In short, for a 100 litre fish tank to reach 3ppm, you would need ~10ml of a 3% solution.

Ammonia Solution	25L Tank	50L Tank	100L Tank
2%	3.8 mL	7.5 mL	15.0 mL
3%	2.5 mL	5.0 mL	10.0 mL
4%	1.9 mL	3.8 mL	7.5 mL
5%	1.5 mL	3.0 mL	6.0 mL
6%	1.3 mL	2.5 mL	5.0 mL

Start by adding 1/2 the calculated dose, then check the circulating ammonia levels with your test kit. Add more ammonia if necessary, until you reach ~3ppm. Make a note of how many ammonia drops (or mL) were needed to reach this level. It’s better to start slow and adjust as you go, to avoid any dramatic spikes.

Step 3: Monitor Ammonia and Nitrite Levels

– After adding ammonia to your aquarium water, start testing your water every 2-3 days (or daily if you’d prefer). After a few days, you should begin to notice some nitrites showing up in your tests. This means that the first group of bacteria is starting to convert ammonia into nitrites. At this point add some more ammonia to the tank – aim for half the amount that you added at the start. Wait another 2-3 days. As nitrite begins to build, it is normal for your ammonia reading to start to decrease.

Step 4: Wait for Nitrites to Drop

– Continue adding ammonia to your tank water every 2-3 days – from here on in only use ~1/4 of the original dose each time. This is because you want to keep feeding the ammonia eating bacteria to keep them alive, but at the moment you don’t have enough bacteria to transform the nitrites. So there’s currently a bottleneck happening in the tank, that needs to be rebalanced. As a result, nitrite levels will spike as the second group of bacteria grows. Again, we want to try to keep this spike below 5ppm if possible, as too high will result in nitrite poisoning of the bacterial colonies. Eventually, the bacteria will convert these nitrites into nitrates.

This stage can take a few weeks, so keep monitoring those levels. The spike should resolve itself pretty quickly, if ammonia dosing has been kept under control. Then you are almost there!

Step 5: Confirm Nitrate Levels

– When both ammonia and nitrites consistently read zero on your test kit, and nitrates are present, your cycle is nearly complete. Before adding any fish, you’ll want to test the cycle (see next step), and also reduce the nitrate levels to below 40 ppm. So, if it’s higher than that, you’ll want to perform a partial water change (most likely your first one of the process – whoohoo!) to bring the nitrate levels down before adding a few fish.

Step 6: Testing the Cycle is Complete / Your Tank Is Ready for Fish

– Once ammonia and nitrites are both zero and your nitrates are at a safe level (<40 ppm), test your cycle is complete. To do this, add the amount of ammonia you did on day 1, to get ammonia to ~3ppm, and see if it has been completely processed within 24h (i.e., ammonia and nitrite should read 0 again 24h after the ammonia is added). If yes, then your tank is fully cycled! You can now add fish gradually, starting with a few hardy fish at a time, to avoid overloading the newly established bacteria while your tank matures.

It may have taken a few weeks, but the result will be well worth the wait!

How Long Does a Fishless Cycle Take?

Patience is key when it comes to a fishless aquarium cycle. On average, the entire process can take anywhere from 4 to 6 weeks, but the exact time frame can vary depending on several factors like the size of your tank, temperature, and the initial levels of ammonia added. And, can be faster again if you add bottled bacteria or seed the tank using some established filter media (see commonly asked questions below for details on how I cut my cycle down to ~3 weeks using this process).

Here’s a general timeline of what you can expect:

Weeks 1-2: Ammonia Levels Rise

After adding ammonia to your tank, the first week or two is typically all about waiting. You’ll notice ammonia levels rising as it builds up in the tank. During this time, you won’t see much change yet with nitrites or nitrates.

Weeks 2-3: Nitrites Appear

As the beneficial bacteria start to develop, they will begin converting the ammonia into nitrites. This is an exciting stage because it means the cycle is progressing. However, nitrites are still toxic to fish, so continue to add ammonia to keep feeding the bacteria while monitoring the levels closely.

Weeks 3-5: Nitrites Peak and Nitrates Begin to Show

The nitrite levels may spike before they start to drop as a second type of bacteria grows, converting nitrites into nitrates. This stage can take some time, and it’s important to keep checking your water parameters to see the changes.

Weeks 5-6: Ammonia and Nitrites Drop to Zero

When both ammonia and nitrite levels finally read zero, it means the bacteria have done their job, and your tank is nearly ready. You should also see a steady rise in nitrates, indicating that there is a presence of the enough bacteria colonies for the full cycle now.

Variations in Timing

It’s important to note that the cycle can sometimes take longer, especially in cooler water, as beneficial bacteria tend to grow more slowly at lower temperatures. Using a filter seeded with bacteria from an established tank (some mature filter media) or some bottled bacteria can speed up the process. Conversely, a lack of ammonia or interruptions in the process can extend the timeline.

Even though the waiting might feel like forever, rushing the process can lead to problems down the road. So try to trust the process and ride it out!

Common Mistakes to Avoid in a Fishless Cycle

Here are some common mistakes to watch out for when conducting a fishless cycle, along with tips on how to avoid them:

1. Adding Too Much Ammonia

– It’s tempting to think that adding more ammonia will speed up the process, but too much can actually overwhelm the bacteria and stall the cycle. Aim for an ammonia level of 2-4 ppm (parts per million) to keep things balanced. Using your test kit to adjust the dosage is the best way to avoid overdoing it. If this gets above 5ppm, it’s recommended to do a partial water change if you don’t see things progressing after a few days.

2. Not Using a Dechlorinator

– Chlorine and chloramine in tap water can kill bacteria including the beneficial bacteria in your fish tank before they have a chance to grow. Always use a dechlorinator before adding water to your tank, even during water changes. This will ensure the environment is safe for bacteria, and later on also for any fish and other aquatic animals you have living in your tank.

3. Skipping Water Tests

– Monitor ammonia, nitrite, and nitrate levels throughout the cycling process. Relying on guesswork can leave you in the dark about the true progress of the cycle. Invest in a good liquid test kit and check your levels at least every other day. This way, you’ll know exactly when ammonia and nitrites reach zero, when to dose more ammonia throughout the cycle and also when it’s safe to add fish. Don’t dose any extra ammonia until you have done a water test, to check where your values are up to and to avoid overdosing.

4. Being Impatient and Adding Fish Too Soon

– One of the most common mistakes is adding fish before the cycle is complete. Even if you see nitrites starting to drop, you need to wait until both ammonia and nitrite levels are at zero. Adding fish too soon can result in harmful spikes, stressing or even killing the new inhabitants and can delay the completion of your cycle. You will have essentially started a fish-in cycle, and will now need to conduct regular water changes to keep the fish alive. However, in doing so, you wil also be slowing down those final steps of the cycle.

5. Not Topping Up Ammonia During the Cycle

– Remember, your beneficial bacteria need ammonia to survive. If you let ammonia levels drop to zero for too long, the bacteria could starve and die off, forcing you to start over. Keep adding small amounts of ammonia every 2-3 days until the cycle is complete to maintain a stable good source for the bacteria.

6. Ignoring Temperature

– Beneficial bacteria grow more efficiently at higher temperatures, around 24-29°C or 75-85°F. If the water is too cold, the cycle can take longer. Using a heater to maintain a consistent temperature will help speed up the process. Just don’t go too hot either – don’t want them to cook!

7. Using Unclean Equipment

– If you’re using any equipment from a previous tank, make sure it’s thoroughly cleaned. Introducing unwanted bacteria or contaminants can disrupt the cycle. It’s always best to start with clean, well-rinsed equipment to ensure nothing interferes with the process.

A little extra attention to detail during these early steps can make a big difference in the long run, giving your fish the best possible start in their new home.

Frequently Asked Questions About Fishless Aquarium Cycling

Fishless cycling can seem a bit daunting for beginners, and it’s normal to have questions along the way. Below are some of the most common questions addressed that people have about the process:

1. How often should I add ammonia during a fishless cycle?

– You should add ammonia as needed to keep the level in the 2-4 ppm range. Typically, this means adding ammonia every 2-3 days, but it depends on how quickly your bacteria are processing it. Keep testing the water and dosing regularly until both ammonia and nitrites drop to zero.

2. Can I cycle my tank faster using bottled bacteria?

– Yes, using products that contain live nitrifying bacteria can help kickstart the cycling process. These can be added directly to your tank and may help speed up the growth of beneficial bacteria. However, results can vary, so it’s still important to monitor your water parameters until you are confident that the cycle has finished.

When I cycled my tank, I used the smallest bottle of Seachem Stability I could find. I dosed daily with a capful until the bottle was empty, then let those little bacteria do their thing. By doing this I figured the tank would have been innoculated with the bacteria strains needed to start consuming both ammonia and nitrite at small amounts, enabling both bacterial groups to have a food source while they developed. For me this process reduced the cycle to just under 3 weeks.

3. Is it normal for nitrite levels to get very high during the cycle?

– Yes, a spike in nitrite levels is a normal part of the fishless cycling process. After the initial bacteria convert ammonia into nitrites, it takes time for the next type of bacteria to grow and start converting those nitrites into nitrates. It can be frustrating, but it means the cycle is progressing as it should. Aim to keep this spike below 5ppm if you can, else it can slow the process down. If you think this has happened and the cycle has stalled for a few days, a small water change can help here.

4. What should I do if my cycle seems to have stalled?

– A stalled cycle can happen if ammonia or nitrite levels remain high for a long time without changing. If this occurs, try doing a partial water change (about 20-30%) to lower the levels in question. Ensure your tank is kept at the right temperature, and double-check that your dechlorinator is working properly when adding new water to the aquarium.

Just a note, sometimes higher values can be hard to read on a water test kit. To gauge if a change to the values is actually happening you can dilute the tank water sample by 50% before you run the test. Then just double the numbers it reads to get the true test result. This can be helpful for reading the results during any spikes.

5. Can I add plants during a fishless cycle?

– Yes, you can add live plants during the fishless cycle, and they can actually help by absorbing some ammonia and nitrites. Just keep in mind that plants may affect how quickly you see changes in water parameters, as they’ll consume some of the nutrients that bacteria would otherwise use.

6. How do I know when my tank is fully cycled?

– Your tank is fully cycled when ammonia and nitrite levels are consistently at zero, and you can dose ammonia up to 2-3 ppm and see it processed within 24 hours. You should also have detectable nitrate levels. At this point, you can do a partial water change to lower the nitrates to below 40ppm and then start adding fish gradually.

7. Do I need to keep the filter running during the cycle?

– Absolutely! The filter is where most of your beneficial bacteria will grow, should be kept running 24/7 during the cycling process – as well as continually after this, for as long as you want the cycle to keep going. This helps ensure proper oxygen levels and water flow, which are necessary for both bacteria and your fish to survive.

A Healthy Start with a Fishless Aquarium Cycle

In summary, completing a fishless cycle is one of the best things you can do for your aquarium and its future inhabitants. Sure, the process might require a bit of patience, but the reward is well worth the wait. Your fish will be free from the stress of toxic ammonia and nitrite spikes, and you’ll have the peace of mind knowing that you’ve given them the best possible start in their new home. Plus, it takes a heap less effort than performing a fish-in cycle!! You’ll also gain valuable insights into water chemistry and the importance of maintaining good water quality—skills that will serve you well as an aquarium keeper.

Remember, every successful aquarium begins with a good cycle. Take the time with the process and soon enough, you’ll be able to sit back and enjoy watching your fish explore their new home.