How To Cycle Aquaponics Without Fish: The Complete Guide

System cycling is crucial during the establishment of a viable aquaponic unit. The process involves introducing and growing a bacterial colony that converts ammonia to nitrates. Fishless cycling has gained popularity among aquaponics hobbyists, but how do you go about it?

Here is how to cycle aquaponics without fish:

  1. Establish your aquaponic unit.
  2. Identify an ideal source of ammonia.
  3. Introduce ammonia into the aquaponics unit.
  4. Monitor the ammonia, nitrite, and nitrate levels.
  5. Add plants and fish to the system.

Fishless cycling is a faster and stress-free method of cycling an aquaponic system. In this article, I’ll discuss how to cycle an aquaponic unit without fish and walk you through all the details and steps. Read on!

1. Establish Your Aquaponic Unit

Cycling can’t proceed if you haven’t finished setting up your aquaponic unit. Establishing an aquaponic system is quite a complex process, and you need to gather all the necessary materials and equipment before you kick-start the procedure. 

Below are the basic requirements for an aquaponic unit and their corresponding functions:

  • A fish tank will accommodate the fish
  • Grow beds are the plant-growing sites
  • Pumps facilitate nutrient delivery and system aeration
  • Mechanical filters sieve out solid wastes
  • Heaters and lighting components provide favorable living conditions for the fish and plants

You may choose to incorporate other things into your system. However, these will depend on your preferred design and the type of aquaponic technique you’ll be practicing. 

You also need to establish an effective plumbing system to ensure that there’s an efficient water flow in your aquaponic unit. The first thing to do is make sure that the plumbing system is well-connected. 

Once you’ve assembled all the materials and equipment, connect all the components to build an aquaponic unit. If you’re a newbie, check the setting up procedure of an aquaponic system here. The process may differ slightly depending on your preferred design.

To set up the system: 

  1. Fill your aquaponic unit with water and let it stay overnight.
  2. If there are some leaks the following day, seal or replace any defective components.
  3. If there’s no leakage, allow the system to run again for 2-3 days.

After setting up the aquaponic unit, you need to determine whether it is ready for cycling.

Measure Your Water’s Quality

Water quality is a crucial issue in aquaponics. You should only use water free from contaminants, chlorine, and chloramine

Rainwater or purified water is preferable in this case. If you’re using tap water (city/municipal), always test it before pouring it in.

If the water contains chlorine, run it in the system for about three days to remove chlorine. Neutralize water with chloramine using humic acid or remove the chemical using activated carbon filters.

It is crucial to have a water quality test kit to monitor the water quality by testing the parameters, such as pH and temperature. 

A water chemistry adjustment kit is also essential in aquaponics. The kit should contain solutions to adjust the water chemistry or ensure that the water has the optimum parameter levels.

For instance, you can have a dechlorinator to remove chlorine in your tap water. The kit may contain a carbonate buffer and acid or base additives to control the pH levels.

After ensuring that your system is good to go, you can proceed with the cycling process.

2. Identify an Ideal Source of Ammonia

Ammonia is the starter in system cycling. It is a compound comprising nitrogen and hydrogen. It also serves as a source of nutrients for ammonia-oxidizing bacteria (AOB).

Since you’re not using fish in this cycling approach, the first and most crucial step is to identify an ideal source of ammonia to cycle your system. Various ammonia sources exist, including natural and artificial ones.

Here are some options that you can consider when obtaining ammonia for system cycling:

Pure Liquid Ammonia

Also referred to as clear ammonia, 100% ammonia, or pure ammonium hydroxide, pure liquid ammonia is the most sought-after ammonia source in aquaponics. It is strictly pure, meaning it has no additives, such as surfactants or perfumes.

This liquid has been used for ages as a cleaning product. You can find it at your nearest hardware or local cleaning products dealer. 

Always go for products that don’t contain additives. The ammonia should also be around 5-10% in weight. To check whether it is pure, first read the product’s description and look out for the words “clear ammonia, 100% ammonia, or pure ammonia.”

You can also shake the bottle. If it foams, the product is pure ammonia.

Pure liquid ammonia is the best option because it is relatively cheap and contains no harmful ingredients. Additionally, you can use it as a cleaning product if you have leftovers. However, it is not readily available in some locations.

Ammonium Chloride

Ammonium chloride is another popular source of ammonia available in crystallized form. It is concentrated ammonia in its solid state. Therefore, you should add a small quantity at a time.

Aquarium hobbyists commonly utilize the product, so there’s probably some sitting on the shelves in your nearest aquarium store. You can also find it in soap or photography supply stores. Like liquid ammonia, the purest form is the best option for cycling.

Organic Fish Fertilizers

Organic fish fertilizers comprise fish-based fertilizers that contain ammonium and nitrogen. If you can’t access pure liquid ammonia from the nearest drugstore, an organic fish fertilizer will come in handy. Apart from providing ammonia for system cycling, these fertilizers are ideal plant nutrients.


Some aquaponics hobbyists use either human or animal urine for cycling their systems. Although it seems gross, urine is a good source of ammonia. However, humans usually excrete their urine as urea, so you’ll have to wait for its conversion to ammonia before adding it to the fish tank. 

You’ll have to store it in sealed bottles for a couple of days (up to 3 weeks) until it converts itself to ammonia. This can be one downside aside from the unpleasant smell. 

Here are the other disadvantages of using urine:

  • Some bacteria and other microbes from your digestive tract may be harmful to the nitrifying bacteria or the fish that you’ll introduce into the system.
  • The quality and quantity of ammonia converted from urea may not meet the threshold required for cycling. Therefore, you’ll need large volumes of urine to meet these demands.

Dead Fish

Although they are not popular sources of ammonia, you can use dead fish during the cycling process. After dying, the fish flesh starts decaying, as facilitated by microorganisms. The decomposition process then produces ammonia.

Using dead fish is a cost-effective approach. However, it is not the most preferred source of ammonia.

That’s because:

  • The decaying flesh can attract other harmful bacteria types (not nitrifying bacteria) into the system. These invaders could pose a risk to the nitrifying bacteria and the fish and can cause the system to collapse.
  • The decomposing fish also attracts flies and other insects to the fish tank. These, too, will disrupt the cycling process.

3. Introduce Ammonia Into the Aquaponics Unit

After identifying the most appropriate source of ammonia, the next step involves adding it into the aquaponic system. 

The introduction of ammonia will attract nitrifying bacteria that will break it down, first to nitrites and then to nitrates, to complete the cycling process. The procedure is not complicated, and you’re guaranteed to have a fully cycled system in about three weeks.

So, what quantity of ammonia do you add to the system?

The amount of ammonia to add to the system will depend on the volume of water that your tank can hold. The recommended ammonia concentration in your fish tank is 4-5 ppm when you’re starting the cycling process. For best results, you should add about 4-5 mg per liter of water. 

If you’re using liquid ammonia, you can add about a cupful on the first day (and note it down). After 60-90 minutes, test the level of ammonia using the API Master Test Kit. If the concentration is below 2.0 ppm, refer to the amount you had initially introduced and calculate the amount you need to obtain 4.0 ppm.

To keep the ammonia levels at 4.0 ppm, add the determined quantity daily for 7 to 10 days. This period will attract the nitrifying bacteria to enable the nitrification process. Monitor the ammonia levels daily.

Now, let’s have a look at how the nitrifying bacteria enable nitrification in aquaponics.

The presence of ammonia in your fish tank attracts two types of nitrifying bacteria. The bacteria usually build a colony inside the biofilter. If your system lacks a biofilter, they’ll create one using the inert media or on the compartment walls.

The first types of nitrifying bacteria are the AOB, including the following:

  • Nitrosomonas
  • Nitrosospira
  • Nitrosococcus
  • Nitrosolubus
  • Nitrosovibrio

These bacteria types get their nourishment from ammonia. They also utilize dissolved oxygen to convert ammonia into nitrite. Both ammonia and nitrites are toxic to fish and are not in a form that plants can uptake. The nitrifying bacteria have to break them down into nitrates.

The second types of nitrifying bacteria are the NOB, including:

  • Nitrobacter
  • Nitrospira
  • Nitrospina
  • Nitrococcus

These break down nitrite to nitrate, completing the nitrification process.

Nitrifying bacteria thrive in warm conditions and environments with high amounts of dissolved oxygen. When you’re setting up your aquaponic unit, ensure that the system is aerated and use warm water (about 80 °F or 26.6 °C). Also, the water’s pH level should be around 7.5 to 8, as the bacteria cannot survive in acidic conditions.

It is preferable to use a bacterial culture at times if your bacterial colony is taking too long to grow. If the conditions are unfavorable, the bacteria could have slow feeding or reproduction rates.

In such instances, you can introduce an established bacterial colony from the following sources:

  • Bacterial ‘seed’ from already established aquaponic system: Obtain some sludge from the biofilter or grow media that contains bacteria.
  • Commercial bacteria: Most aquarium stores sell live bacterial colonies. Introducing these bacteria will speed up the growth of a colony in your system and quicken the cycling process. 

4. Monitor the Ammonia, Nitrite, and Nitrate Levels

It is vital to monitor the ammonia levels in your aquaponic system daily.

In the first couple of days, the ammonia concentration should be around 4-5 ppm. At this point, the AOB will inhabit the system and start breaking down the ammonia to nitrite.

After ten more days, the ammonia levels in your fish tank will start declining. Your daily parameter tests will reveal reduced ammonia concentration, and you’ll begin to detect some nitrite on the test strips. 

If the ammonia concentration drops below 0.5 ppm, you should add about three-quarters of the original quantity to keep the AOB alive and well-nourished.

In the next ten days, the nitrite levels will increase steadily, indicating that the nitrifying bacteria (AOB) have converted almost all the ammonia to nitrite. Keep testing for ammonia and nitrite. 

When this conversion process is complete, you’ll notice almost no amounts of ammonia and increased nitrite levels.

The nitrite levels will start reducing in the next 10-15 days, indicating that a colony of nitrite-oxidizing bacteria is living in your aquaponic unit. Continue testing for nitrite, as you also start testing for the presence of nitrate. The nitrite levels will approach zero in a few days, while the nitrate concentration will rise above 5.0 ppm.

At this point, the cycling process is almost complete, meaning that your system is now ready for food production.

5. Add Plants and Fish to the System

Although you can introduce plants at the beginning of the cycling period, this will require you to add fertilizers to the growing beds manually. Adding plants and fish is preferable after cycling is complete. You can plant your seeds in a nursery earlier to ensure that the seedlings are ready when cycling is over.

Before introducing fish or plants to the system, ensure that the parameters are favorable for survival and growth. 

For instance, ammonia and nitrite levels should be below 0.5 ppm, while the nitrate concentration should be 5-10 ppm. Also, ensure that the fish stocking density matches the plant volume to avoid an imbalanced system.

To maintain a balanced system, ensure that the plants’ nutrient requirements match the stocking density. These factors will also determine how much you feed the fish and the amount of waste they’ll produce. I recommend calculating the fish feed rate ratio to know how much feed you’ll be introducing into the system daily.

Depending on your location’s environmental conditions, your preferences, fish breed availability, or local regulations, you can add various fish species to your unit.

Note: It is crucial to acclimate your fish before introducing them into the system. Doing so will minimize fish stress and mortality rates.

After adding fish and plants to the system, it’s advisable to continue monitoring the parameter levels to determine if the biofilter is well-established.

If you notice an upsurge in ammonia and nitrite concentrations (above 0.5 ppm), this means the fish wastes exceed what the nitrifying bacteria can handle. In that case, minimize the number of fish feeds or do partial water changes to remove excess ammonia.

Conversely, if the ammonia, nitrite, and nitrate levels are below 0.5 ppm, it means that your plants’ nutrient uptake has exceeded the system’s production, and you need to increase the fish feed.

However, if only ammonia is present, the pH levels could be too low for the nitrifying bacteria, so you’ll have to increase them to a pH of 8.

System Cycling Basics

Cycling is paramount when setting up an aquaponic system. However, before we dive into the benefits of fishless cycling, we need to understand the principle behind cycling and how it works.

Let’s take a look at what cycling entails.

Cycling is a process that involves the introduction and buildup of a bacterial colony in aquaponics. The bacteria have a vital role in the system, as they bridge the gap in the symbiotic interaction between the fish and the plants. 

The bacteria help break down the fish wastes and other organic matter that accumulates in the fish tank and convert this waste into beneficial plant nutrients.

The bacteria comprise the biofilter in aquaponics since they participate in biofiltration. Two types of nitrifying bacteria, including ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), are involved in system cycling. These microbes facilitate a nitrification process to form a nitrogen cycle.

Role of Nitrification in Aquaponics

Nitrification is vital in aquaponics, as it aids in waste management and nutrient cycling. 

An aquaponic system requires ammonia and nitrates to thrive. Ammonia is a by-product that results from fish wastes and decaying organic matter in the fish tank. However, it is toxic to the fish when it accumulates to more than 0.5 ppm (parts per million).

Although ammonia is a nitrogenous compound, it is not beneficial to plants in that form. Therefore, it has to be converted to nitrates, which plants can uptake efficiently. That’s where the nitrifying bacteria come in, as they facilitate this conversion process.

Ammonia is the first component in the nitrogen cycle. To cycle your aquaponic system, you need to introduce ammonia to the system first. Two cycling methods exist, depending on the ammonia source.

They include:

  • Fish cycling involves introducing sacrificial fish to produce ammonia into the system. The commonly used fish breed is the Goldfish since it is cheap and readily available.
  • Fishless cycling entails using other ammonia sources other than fish to start the cycling process. It is preferred because it takes a shorter duration than fish cycling.

Since this article will focus on fishless cycling, let’s explore the method’s benefits.

Benefits of Fishless Cycling

Less Stress

Fishless cycling poses less stress to the fish and the farmer. The fish don’t have to experience ammonia spikes (that could be fatal) because the method utilizes an alternative source of ammonia.

The system’s owner also doesn’t experience stress due to the loss of fish. Moreover, pH variations are a non-issue since there are no fish in the system.

Faster Speed

Fishless cycling is faster than fish cycling. While fish cycling takes 6 – 8 weeks, you can complete fishless cycling within 10 – 21 days. You’ll incur lower start-up costs, as your system will start running sooner and producing food.

Quicker Bacterial Growth

Since you can increase the ammonia concentration to harmful levels (if it were in fish cycling), establishing and building a bacterial colony takes less time.

Additionally, the system attains a  balance sooner, enabling the farmer to have a larger fish stocking density at once, minimizing aggressive behavior in fish (especially the carnivorous types).

Final Thoughts

Fishless cycling is an effective way of establishing a bacterial colony in your aquaponic system. It is faster than fish cycling and minimizes fish stress experienced when ammonia and nitrite levels spike.

So, in summary, to cycle your system without fish, these are the steps to follow:

  1. Establish your aquaponic unit.
  2. Identify an ideal source of ammonia.
  3. Introduce ammonia into the aquaponics unit.
  4. Monitor the ammonia, nitrite, and nitrate levels.
  5. Add plants and fish to the system.

Alexander Picot

Alexander Picot is the founder of and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

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