Goldie fish in a tank

How to Cycle a Fish Tank With and Without Fish

One of the first rules of fishkeeping is maintaining your ammonia levels. Contrary to what many new fishkeepers might believe, you can’t simply get a new aquarium, fill it with water, and place a couple of fish in it. You need to cycle the fish tank first, to ensure that it’s safe for your fish to live in. If you expose your fish to misread nitrogen cycles, they’ll fall ill and die.

I’m a fishkeeping expert who has tried and tested several quirks to achieve the perfect nitrogen cycle. Throughout my years, I’ve perfected the ideal method for fishless and fish-in cycles (even though I’m not a big fan of the latter).

To help you, I’ve created this comprehensive guide with my tips and how-tos for each method, the pros and cons, and how to maintain your freshly cycled aquarium.

Understanding the Nitrogen Cycle

The nitrogen cycle refers to the transition of ammonia to nitrites, nitrates, and nitrogen gas. 

For your fish’s safety, their aquarium needs beneficial nitrifying bacteria to remove all the aquarium’s waste. So, nitrifying bacteria directly carries out the nitrogen cycle.

Here are the three main parts of every aquarium nitrogen cycle:

Ammonia Addition

The first step occurs when you add ammonia into the fish tank

In a fishless cycle, you’d manually add ammonia into the aquarium with a dropper. For fish-in cycling, you can choose to drop pure ammonia or rely on your fish’s waste. 

I also learned about a shrimp method, in which you add a jumbo shrimp into the tank and let it do its bacteria-attracting magic as it decomposes. I tried it and it works, but you’ll need some surface agitation to oxygenate the water and prevent odor.

Ammonia Decline – Nitrite Spike

This process is also called nitrification,  where bacteria convert ammonia to nitrites.

The ammonia spike will result in a bacteria-consuming bloom, which will then cause a sharp decline in the tank’s ammonia. 

Nitrite Decline – Nitrate Spike

Nitrobacter bacteria then convert nitrites to nitrates, which are plant nutrients. In this stage, you’ll perform a large water change to remove the nitrate build-up and make the tank habitable for your fish. 

At this stage in a fishless cycle, I prefer to perform a 50% water change to cut the nitrates to non-toxic levels.

🐠 Grasp the essential process that keeps your tank healthy. Dive deeper into understanding the nitrogen cycle with our detailed breakdown.

Preparing to Cycle Your Tank

When preparing to cycle your tank, you’ll need the following materials:

  • An ammonia source: For both fishless and fish-in cycling, you’ll need some form of ammonia. I’d recommend DrTim’s Aquatics Ammonium Chloride since it is specially formulated for aquarium use.
  • A high-quality water filter (You can also use pre-established filter media from another tank).
  • An aquarium test kit: An aquarium test kit measures the four most important water parameters including pH, ammonia, nitrite, and nitrate.
  • Conditioner: Adding conditioner to the tank water helps to remove chlorine, which kills the good bacteria you’re looking for. I use API Stress Coat Water Conditioner because it safeguards my fish by replacing their protective coat.

How to Cycle a Fishless Fish Tank

It takes anywhere from four to six weeks to cycle a fishless tank. It isn’t as risky as fish-in cycling, so I prefer to perform a fishless cycle. But while it has its perks, it isn’t free from disadvantages.

Here are the pros and cons of cycling a tank without fish:


  • It’s faster because you can introduce more ammonia into the tank to create larger bacteria colonies.
  • It broadens your fish options because you aren’t cherry-picking hardy species to survive the cycling process.
  • You can avoid stressing your fish during the process.
  • You can decorate your aquarium with beautiful live plants that may not survive fish-in cycling.


  • You can’t add your fish right away and instead have to wait till the tank is established.
  • There’s no immediate biological load, so you have to manually add ammonia. For instance, fish-in cycling derives its ammonia from fish waste.

Steps for Cycling a Tank Without Fish

Here’s how to cycle your tank without fish.

Set Your Tank Up and Increase the Temperature

After setting up your tank with pre-conditioned water, your cycle’s success largely relies on your filter because it’ll host beneficial bacteria. You should also increase the tank’s temperature to around 85F to support your incoming colonies.

🐠 Choosing the right filter is crucial for a successful cycle. Find the top picks in our guide to the best aquarium filters on the market. Discover the best aquarium filters.

Introduce Ammonia

Using a dropper, add pure ammonia into your tank until you reach 4 ppm. Start gradually and don’t be afraid to perform a partial water change in case of an overdose. 

Here, I like to keep a journal and note the amount I used to achieve my results. It helps me dose the ammonia better and perfect my cycling process.

Add Tank Supplies

If you have any live plants and gravel, now’s the time to add them in since they appreciate the nitrate-rich environment. You get bonus points if you remove the plants from an established tank because they carry beneficial bacteria.

Monitor the Ammonia Levels

Begin testing your water parameters daily to monitor the ammonia levels. If it goes down to 1 ppm, add ammonia with a dropper to crank it up to 4 ppm. From the third or fourth day, you can start testing for nitrites.

Nitrite levels can take anywhere from 3-6 weeks to peak, and during this period you should test for nitrates daily. Around the fifth or sixth week, nitrite levels should crash and nitrates should increase. This tells us that it’s time for a 50% water change.

Once more, introduce ammonia into your tank until it reaches 4 ppm. Your tank’s bacteria should consume the ammonia in 24 hours, causing you to read 0 ppm the next day. Your tank’s cycle is now complete and ready to house fish.

How to Cycle a Fish Tank with Fish

Cycling a tank with fish is a more delicate process than fishless cycling because your fish are vulnerable to spikes in ammonia. 

Unfortunately, I’ve lost a few buddies in my beginner days of nitrogen cycling. But, you can certainly perform a fish-in cycle with minimal damage. If you’re a beginner, I recommend doing a fishless cycle.

Before cycling your aquarium tank with fish, here are the pros and cons you should consider: 


  • You can get fish into the aquarium right away.


  • You’re likely to stress your tank’s occupants, including plants.
  • If you lose any fish, it leaves behind harmful bacteria.

Steps for Cycling a Fish-in Tank

Set Up a Filtration System

To jumpstart the cycling process, you must ensure that your tank is properly set up. So, you should have a good filter, gravel, pump, and heater. The main task is to keep the fish alive and well throughout the process.

Add Hardy Fish

Fish-in cycling is a process that even healthy fish won’t tolerate. For this reason, you should add a few hardy fish like tetras, since they can withstand quality fluctuations. Remember not to add too many fish to avoid an ammonia overload.

Add Ammonia 

When performing a fish-in cycle, you can use fish feed or pure ammonia. However, using pure ammonia runs the highest risk of a spike, so I’d recommend cycling with feed. 

To prevent excess ammonia buildup, you should only feed a small amount to your fish. I’d recommend feeding one pellet per fish.

Monitor Levels and Fish Behavior  

Test the tank’s ammonia levels every 1-2 days to ensure that it remains below 0.5mg and the nitrite is below 1 mg per liter. The cycle is complete once your tests read 0 for both ammonia and nitrite levels. However, you should add a maximum of two fish at a time and follow a 7-day interval.

🐠 Ensure your fish thrive during the cycling process. Learn the best ways to acclimate your fish with our expert advice.

Testing Water Quality

Certain parameters indicate your tank’s water quality and tell you how safe your fish are in their tank. They are:

  • Temperature: Not all fish fare well under the same temperatures, so monitoring it can prevent sickness and death. It can also help you tame parasites like ich.
  • pH: pH measures how acidic or basic your tank water is, forming a crucial part of water quality. For instance, a pH below 6 keeps pure ammonia as ammonium, which is unusable for nitrifying bacteria.
  • Ammonia: Ammonia attracts useful bacteria, but it’s also detrimental to fish in excess.
  • Nitrite: Nitrite is a toxic form of nitrogen, which is broken down by plants or removed during water changes.
  • Nitrate: Nitrates are formed during the final process of the nitrogen cycle. It’s the least toxic form of nitrogen, but it can affect aquatic life at high levels.
  • Alkalinity: High alkalinity (9.6 and above) can affect your fish’s gills and skin and influence their metabolic processes.
  • General hardness: General hardness measures the magnesium and calcium levels in your tank water. It heavily affects the tank’s pH and influences osmoregulation.

How to Test and Interpret Water Quality  

After purchasing your test kit, read the instructions and rinse your vials. Then, take a cup of water from the aquarium and begin testing one parameter at a time.

Write down the results for each test and compare them with the regular range. This exam will give you insight into what is ailing your fish and help you to tackle it. Repeat this test every day for a week or until your aquarium readings are within normal range.

Maintaining a Cycled Aquarium

Cycling your aquarium is only the first bit to creating a safe aquatic habitat. The real deal is how you maintain your tank.

Here are some regular maintenance practices to keep your newly cycled aquarium healthy:

Regular Testing and Water Changes

Regularly testing your tank water diagnoses potentially harmful parameter levels and enables you to adjust nutrient levels by changing the tank water. I’d recommend performing a 25% water change every 2-3 weeks.

Maintaining Filtration Equipment

Cleaning your tank filter refers to removing decaying debris. So, you’ll need to disassemble it into clean aquarium water and rainwater to dislodge the trapped dirt. You should never use bleach or soap on your aquarium filter to avoid killing the good bacteria and harming your fish. 

Manage Algae Growth

Algae overgrowth is a direct result of excess ammonia, so it is important to have a hands-on approach to managing your tank’s algae. You should always have an algae film but I recommend scraping once a week to manage overgrowths.

Cleaning Your Fish Tank

Aim to clean your fish tank (including gravel) every three weeks. However, if you own a large tank, you get away with cleaning once a month.

Tips for Troubleshooting Common Issues Post-cycling

Ammonia Levels Won’t Drop

Stable ammonia levels indicate an absence of good bacteria. This issue can result from below-6 pH levels (because the bacteria can’t use ammonia in that state) and using tap water.

Algae Overgrowth

After cycling, if you encounter an algae problem, scrape and turn off the lights because direct sunlight encourages algae growth. If you have aquarium plants, the problem may be over-fertilization.

Your aquarium is Cycling Again

Sometimes, after a major change, your aquarium will start to recycle. This is caused by suddenly adding too many fish, overwhelming the bacteria, and causing a new ammonia spike. You can stop this problem by restocking and acclimating your fish gradually.

Cycling a Healthy Habitat

The nitrogen cycle is essential to both fishless and occupied tanks because it provides healthy waste-consuming bacteria. By monitoring your tank’s ammonia, testing accurately, and performing regular water changes, you can cycle your tank with minimal harm.

Remember that beginners often have a trickier experience with their first cycle, but it shouldn’t deter you from continuing the process. You can’t fail till you abandon it!

Do you prefer the fishless or fish-in method when cycling your fish tank? Tell us why in the comments, and share this article with a fellow fishkeeping hobbyist!

Frequently Asked Questions 

How Long Does it Take for a Fish Tank to Cycle?

On average, it takes 6 weeks to fully cycle a tank. However, the tank’s size, temperature and pH can affect the total duration. For example, a tank pH of 7.0-7.8 and a temperature of 83 F- 87 F can speed up the process and ensure a safe environment for your fish.

How Do You Cycle a Fish Tank for Beginners?

The fishless method is the safest way for absolute beginners to cycle a fish tank. You’ll need ammonia, conditioners, water filter, and a test kit. Then, start by adding ammonia into the pre-conditioned tank water, and test daily for cycle progression. After 4-6 weeks of regular testing, slash the ammonia levels with a 50% water change.

Do You Need to Do Water Changes When Cycling a Tank?

You need to perform frequent water changes when cycling an aquarium with fish. Even for a fishless tank, water changes help prevent ammonia and nitrite levels from overwhelming your new bacteria colony. However, you only need to perform water changes every few days in a fishless tank. 

What Are The Best Fish to Cycle a Tank With?

The best fish to cycle a tank with are bettas, guppies, and dwarf gouramis. These are especially hardy species that can withstand imbalances without taking ill or dying. Some hobbyists even use these fish to test the water after a fishless cycle before introducing other fish.

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