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Writer's pictureHarold Lim

The Best Way to Cycle a Fish/Shrimp Tank: A Step-by-Step Guide for Beginners

Setting up a new aquarium is an exciting process, but before adding any fish or shrimp, it's crucial to cycle the tank properly. Cycling ensures that beneficial bacteria establish in the tank, helping to break down harmful waste products like ammonia into less toxic forms. Without a proper nitrogen cycle, your tank's inhabitants could face stress, illness, or even death.


This guide will walk you through the best methods to cycle your tank effectively, explain why cycling is so important, and offer tips for ensuring success.


What is Tank Cycling?


Tank cycling is the process of establishing a colony of beneficial bacteria (known as nitrifying bacteria) in your aquarium filter, substrate, and surfaces. These bacteria convert toxic ammonia, which is produced by fish waste, uneaten food, and decaying organic matter, into less harmful nitrite, and then into relatively harmless nitrate.


The nitrogen cycle has three main stages:


  1. Ammonia (NH3) is produced by waste and decaying matter.

  2. Nitrosomonas bacteria convert ammonia into nitrite (NO2), which is also toxic.

  3. Nitrospira bacteria convert nitrite into nitrate (NO3), which is much less harmful and can be managed with water changes and plants.


Why Is Cycling Important?


In a new tank, there are no established bacteria to process ammonia. If you add fish before the tank is cycled, the ammonia levels can spike, causing “New Tank Syndrome,” which is harmful and often fatal to fish. Cycling your tank before adding fish ensures a stable, healthy environment where waste products are processed safely.


Methods to Cycle a Tank


There are several ways to cycle a tank, but the following three methods are the most reliable:


1. Fishless Cycling (Recommended)

Fishless cycling is the safest and most humane method because it doesn’t expose fish to toxic ammonia or nitrite during the process.


How to Perform Fishless Cycling:


  • Step 1: Set Up Your Tank

    Set up your aquarium with a filter, heater, substrate, and decorations. Add dechlorinated water to fill the tank. If you plan to use live plants, you can add them now as they help absorb some ammonia and nitrate.


  • Step 2: Add a Source of Ammonia

    You'll need a source of ammonia to kickstart the cycle. There are several methods you can use:

    • Pure Ammonia: The most controlled way to cycle a tank is by adding pure, unscented ammonia (available at hardware stores). Add small amounts to reach a concentration of about 2-4 ppm (parts per million). Use a test kit to measure the levels.

    • Fish Food: Another option is to add a small pinch of fish food to the tank daily. As the food decays, it releases ammonia, although this process is slower and less controlled than using pure ammonia.


  • Step 3: Test the Water

    After adding ammonia or a source of decay, test the water daily using a liquid test kit to measure ammonia, nitrite, and nitrate levels. Within a few days to a week, you should start to see nitrite appear as ammonia is converted.


  • Step 4: Wait for Nitrite to Spike and Fall

    As bacteria begin to convert ammonia into nitrite, nitrite levels will rise and then fall as more bacteria develop. This process can take several weeks.


  • Step 5: Nitrate Appears

    Once nitrite is converted into nitrate, you'll see nitrate levels rise. Nitrate is less harmful but should still be kept in check with water changes. When ammonia and nitrite reach 0 ppm, and nitrates are present, your tank is cycled.


  • Step 6: Perform a Water Change

    Before adding fish, do a 50% water change to reduce nitrate levels to below 20 ppm.


  • Step 7: Add Fish/Shrimp

    Now that the tank is fully cycled, you can slowly add fish, a few at a time, to avoid overwhelming the bacteria.


2. Fish-In Cycling (Only If Necessary)


This method is more stressful for fish and should only be used if you already have fish in an uncycled tank or are unable to do fishless cycling.


How to Perform Fish-In Cycling:


  • Step 1: Set Up Your Tank

    Set up the tank as usual, including the filter, heater, and decorations.


  • Step 2: Add a Few Hardy Fish

    Introduce a small number of hardy fish, such as Zebra Danios or Cherry Barbs, which can tolerate less-than-ideal water conditions. Avoid sensitive species.


  • Step 3: Monitor Ammonia and Nitrite Levels

    Use a test kit daily to monitor ammonia and nitrite. These levels will rise during the cycle, so it’s important to take action to prevent toxic buildup.


  • Step 4: Perform Frequent Water Changes

    Do frequent, small water changes (10-20%) every day or every other day to keep ammonia and nitrite levels below 0.5 ppm. Make sure to dechlorinate the water before adding it to the tank.


  • Step 5: Add Bacteria Supplements

    You can add bottled bacteria supplements to help seed the tank with beneficial bacteria. This can speed up the cycling process and reduce stress on your fish.


  • Step 6: Complete the Cycle

    The tank is cycled when ammonia and nitrite levels drop to 0 ppm, and nitrates start to build up. Once this happens, continue to perform regular water changes to manage nitrate levels.


3. Using Established Filter Media or Substrate


This is the quickest way to cycle a tank if you have access to an established aquarium.


How to Use Established Filter Media:


  • Step 1: Obtain Established Media

    Ask for filter media or substrate from a mature, healthy tank. This material already contains colonies of beneficial bacteria.


  • Step 2: Add to Your New Tank

    Place the mature media in your new filter or mix it into your substrate. This will seed the tank with beneficial bacteria, jump-starting the cycle.


  • Step 3: Add a Source of Ammonia

    Like with fishless cycling, add ammonia or a few fish to begin the cycle.


  • Step 4: Monitor Progress

    The cycle will proceed faster than starting from scratch, but you’ll still need to test ammonia, nitrite, and nitrate levels regularly to ensure the cycle is complete.


How Long Does Cycling Take?


The cycling process can take anywhere from 2 to 8 weeks, depending on your method, water temperature, and whether you’re using bacteria starters. Fishless cycling is usually faster when using bottled bacteria or established media, while fish-in cycling may take longer due to the need for slower ammonia buildup.


Signs That Your Tank is Cycled:


  1. Ammonia Levels at 0 ppm – There should be no detectable ammonia in the tank.

  2. Nitrite Levels at 0 ppm – Nitrite should also be undetectable.

  3. Nitrate Levels Rising – Nitrate will be present, usually between 5-20 ppm.

  4. Stable Water Parameters – After testing for several days, your ammonia and nitrite levels remain at 0 ppm without fluctuating.


Tips for a Successful Tank Cycle


  • Be Patient: Rushing the process can harm your fish or shrimp. Give the bacteria time to establish.

  • Use a Test Kit: Liquid test kits are more accurate than strips and will help you monitor the cycle’s progress.

  • Don’t Overfeed: Excess food can break down into ammonia, making the cycle harder to control. Feed fish sparingly.

  • Add Plants: Live plants can help absorb excess nitrates and improve water quality.

  • Avoid Cleaning Too Much: Don’t clean the filter or change too much water during the cycling process. The bacteria need time to settle and grow.


Conclusion


Cycling a fish tank is the foundation for a healthy and thriving aquarium. While it may take some time, properly cycling your tank ensures that harmful toxins are processed efficiently, creating a safe environment for your fish, shrimp, or other aquatic life. By following the steps outlined above and practicing patience, you'll have a fully cycled tank ready for new inhabitants in no time. Happy fish or shrimp keeping!

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