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How to Cycle a Fish Tank with Fish Food: Full Method Explained

A pile of fish food flakes.

It’s possible to cycle a fish tank with fish either in or out of the tank. Cycling is a term used in fish keeping for growing bacteria levels high enough to consume the ammonia produced by fish. In this article, I will explain how to cycle a fish tank with fish food, but first a quick summary of the overall process for how to do it.

To cycle a fish tank with fish food, add 0.17 oz (5 grams) of fish food per 15 gallons (56.8 liters) of water in a tank filled with regular tap water. Wait for about 1 week for the fish food to decompose into ammonia, and test the ammonia levels with a water testing kit, then add beneficial bacteria. 

The entire process is a little bit tricky to understand, so below I’ll explain:

  • exactly what is happening when you are cycling a fish tank
  • how to cycle a fish tank using this method
  • a detailed step-by-step instructions for how to cycle a fish tank using fish food
  • the pros and cons of using fish food to cycle a tank.

How Long Takes To Cycle a Tank With Fish Food & Step-by-Step Instructions

Cycling a fish tank with fish food is not the fastest method but is also not too much slower than other methods for cycling a fish tank. Here is how long it takes to cycle a new aquarium using fish food.

As a general rule, it takes 4 weeks to cycle a fish tank with fish food. First, the fish food needs to decompose, which takes about 1 week. Then beneficial bacteria should be added. After about 3 weeks the beneficial bacteria levels are high enough for a tank to be cycled.

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Once the bacteria numbers are sufficiently high enough they will process all of the ammonia down to zero. Then it’s safe to say that they will keep up with the ammonia produced by live fish in the tank.

The overall steps to cycle a fish tank with fish food are:

  1. Get everything required ahead of time.
  2. Add the fish food to the tank.
  3. Measure the ammonia levels.
  4. Add the beneficial bacteria.
  5. Measure the ammonia levels.

Before explaining each step in detail it’s important to know if cycling a fish tank with fish food is the right method for you. 

There are a few drawbacks to cycling a tank with fish food. It’s a fun experiment to try. But, if you are just interested in cycling a fish tank the easiest way then fish food is a little bit unreliable.

The best method in my opinion is to use pure ammonia instead. The reason is, it’s far easier to measure exactly what the ammonia levels will be. On the other hand, when using fish food you need to somewhat guess how much ammonia will be produced and present in the water.

When you add fish food it needs to break down for the ammonia to be produced, then there are multiple factors that control how much ammonia is released. 

When cycling a fish tank it’s best to start with ammonia levels within the range of 4 ppm to 8 ppm. But, if the amount of ammonia produced by the fish food ends up being too low, then you will need to wait another week before enough ammonia is present in the water.

A close up of brightly colored fish food flakes, that are orange, red, and brown.
When fish food breaks down in the water it produces ammonia

Below, I have provided fairly accurate amounts of fish food to add to a tank based on how large the tank is. But, there’s no way to guarantee how much ammonia you’ll have in the tank after one week.

NOTE: The only way you can precisely control exactly how much ammonia you are starting with is to use 100% pure ammonia.

#1: Get Everything Required Ahead of Time

There are a few things you will need to cycle a fish tank. It’s best to have these ahead of time, as some can take a bit of time to source. That way you can breeze through all of the steps, without needing to delay one or more of the steps while waiting on any of these items.

The things you will need are:

  1. Fish food: try this one from Amazon (1 to 2 oz is enough unless you have a very large tank).
  2. Water testing kit – have a minimum of 3: find them here on Amazon.
  3. Live bacteria liquid (this one on Amazon is a great choice), or items from an established tank (explained below).
  4. A water filter: sold here on Amazon.
  5. Heaters (optional): this one from Amazon is a great value.

Studies have shown that the beneficial bacteria present in aquariums grow best when the water temperature is above room temperature. The water temperature at which they grow best is 86 to 95 °F (30 to 35 °C). Whereas, water at room temperature is 78 °F (25.5 °C).

If you are setting up a tropical fish tank then you will be getting water heaters to keep the water warm enough. Otherwise, it’s not necessary to get heaters. It will make it faster but not significantly, so it’s not worth getting them just to cycle your fish tank.

Getting Some Items from an Established Tank

It’s common to use items from an established tank as the source of beneficial bacteria for a new tank. The beneficial bacteria will begin to grow on their own, but adding some items from an established tank will start a tank off with a lot of bacteria and it will increase at a faster rate.

Getting these items if you don’t already have them can be a bit of a task. You can ask friends and family who have fish tanks, or experienced fish keepers. They typically have a few extra sponges in their water filters that they will be willing to donate or sell to you for a very low price.

Joining your local fish keepers club is a great way to meet other fish keepers, and they will generally always be willing to help out with some extra sponges to help you get your first tank started.

#2: Add the Fish Food to the Tank

There is a specific amount of fish food that should work well to add enough ammonia. As mentioned earlier, using the fish food method is not as precise as adding pure ammonia. 

Therefore, the numbers below are not very rigid and if you use a little more or a little less it won’t have a significant effect.

There are many different sizes of fish tanks. The general ranges are:

  • Small – 2.5 gallons to 15 gallons (9.5 liters to 56.8 liters)
  • Medium – 20 gallons to 45 gallons (75.7 liters to 170.3 liters)
  • Large – 50 gallons to 225 gallons (189.3 liters to 851.7 liters)

To know how much fish food to add you need to do a rough calculation. The rule for a tank 15 gallons or smaller is to add 0.17 oz (5 grams) of fish food. 

This is equal to about 14 pinches of fish food. Commonly when feeding fish you take a pinch of fish food and add it to the tank. So, using the pinch method is an easy way to measure it.

If a tank is 30 gallons add 0.34 oz (10 grams) of fish food since 30 gallons is 2 times a 15-gallon tank.

The calculation you need to do is:

  1. The number of gallons in your tank, divided by 15
  2. Whatever, the number you get from the first step, multiply it by 0.17 oz (5 grams)

Here’s an example, so you can see how to do the calculation. 

  • Suppose you have a fish tank that is 45 gallons. 
  • You divide 45 gallons by 15 (this is step 1). This equals 3
  • You then multiply that number by 0.17 oz (or 5 grams) which is 0.51 oz (15 grams). 

If you don’t have scales, an easy way to measure how much fish food to add is to use pinches of fish food.

A woman adding a pinch of fish food to a fish tank.
Measure the amount of fish food to add in pinches

0.1 oz roughly equals 1 pinch of fish food. In the example above, the amount of fish food to add to a tank is 0.51oz. Which is equal to 51 pinches of fish food. Add it all at once or over a day or two, both methods work just fine.

NOTE: It’s a good idea to mix the fish food around the tank or spread it out as you add it. Doing so will help it break down faster because the food will have more surface area in contact with the water.

#3: Measure the Ammonia Levels

After one week, you should measure the levels of ammonia in the water. At this time, the fish food will have mostly decomposed and released ammonia into the water.

This is done using a water testing kit (this one from Amazon is great value). The amount of ammonia should be over about 4 parts per million (ppm), but anywhere in the range of 4 ppm to 8 ppm is good

If there is more ammonia in the tank it’s not a big issue but it will take longer for the beneficial bacteria to break it all down. Once there is sufficient ammonia in the tank then you can add the beneficial bacteria to the tank. 

#4: Add the Beneficial Bacteria

In this step, we add starter beneficial bacteria. Bacteria grow incredibly quickly. According to the Pacific Northwest Laboratory, the number of bacteria doubles every 4 to 20 minutes. It varies based on the species of bacteria.

It’s widely established by fish keepers that if you don’t add starter bacteria, cycling a fish tank can take 6 months or more. Therefore, it’s thoroughly recommended by experienced fish keepers to add beneficial bacteria manually to cycle a tank.

This can be store-bought live liquid bacteria or items from an established fish tank. It’s reported that some liquid bacteria you buy in stores are not very effective since they don’t contain live bacteria.

Any brand of live bacteria should work, but the one that is love is the Fritzyme 7 Freshwater Live Bacteria (Amazon link). It’s great value and high quality.

The other option is to add items from an established tank as mentioned above about where to get these from. Either method is fine. Choose the method you want to use and add the bacteria to the tank. It will then begin to grow.

After about 2 weeks the number of bacteria should be high enough to consume most of the ammonia that you added and will have the capacity to consume enough ammonia that it’s safe to add fish. But, the levels of ammonia should be measured to be sure.

An established fish tank with a lot of plants and fish.
Using items from an established fish tank builds live beneficial bacteria

#5: Measure the Ammonia Levels (For a Second Time)

For your fish tank to be completely cycled the nitrogen should be near 0 ppm, and definitely below 1 ppm. Use another water testing kit and see what the ammonia levels are. If they still aren’t below 1 ppm, then wait another week or so

Waiting will give the bacteria more time to grow in numbers, and also consume the ammonia in the tank. If it’s under about 0.5 ppm then it’s safe to add a few fish.

It’s a good idea to only add a few fish at a time, and wait for 3 to 4 days to a week before adding more fish. After you add them, observe them to make sure they are doing OK. If you want you can retest the ammonia levels again after about a week, or before adding more fish.

Provided you’ve done everything above, there should be plenty of beneficial bacteria to easily handle the ammonia produced by a few fish, and the bacteria will continue to increase in number

NOTE: If there is not enough ammonia in the tank, some bacteria will die. Naturally, the total bacteria in the tank will stabilize based on the amount of ammonia produced by the fish.

How Do You Cycle a Fish Tank Naturally

Cycling a fish tank is required before placing fish into a tank, otherwise, it can cause your fish to have health issues. It’s possible to cycle a fish tank naturally without adding artificial chemicals. Here’s how to cycle a fish tank naturally.

Use fish food or pure ammonia. To cycle a fish tank, ammonia needs to be present in the water for beneficial bacteria to grow.  Fish food breaks down and releases ammonia, and pure ammonia is also a naturally occurring chemical present in nature. 

Ammonia is a chemical compound that has 1 nitrogen atom and 3 hydrogen atoms and is created by fish naturally. It has the chemical formula NH3. Whether ammonia is pure ammonia produced in a lab chemically, or ammonia found in nature it has the same chemical structure. 

FUN FACT: Artificially created ammonia and naturally created ammonia are interestingly the exact same thing since they have the same chemical formula.

Tap water is recommended for fish tank water but contains virtually no ammonia. As a result, ammonia needs to be added to the water in some way to cycle a fish tank.

An empty fish tank with a blue light.
Cycling a fish tank can take weeks or months

How To Cycle a Fish Tank in One Day

Cycling a fish tank typically takes a few weeks to a month. However, while a fish tank is cycling it’s not recommended to have fish in the tank as it will stress them. So, cycling a fish tank sooner rather than later is better, here’s how to cycle a fish tank in one day. (It’s as article I wrote for those of us with a little less patience!)

Add pure ammonia to the water to make the ammonia levels in the water between 4 ppm to 8 ppm, then add as many live beneficial bacteria as possible. Below is a detailed explanation of how to do it.

Typically, it’s VERY difficult to cycle a fish tank in one day. 3 to 4 days is realistic but can be a stretch. 

I have explained exactly how many drops of pure ammonia to add to a tank in this article about how to cycle a fish tank with ammonia. The amount of ammonia to add depends on the size of the fish tank – which is how much water is in the tank.

Cycling a fish tank with ammonia is the fastest method to cycle a fish tank. To cycle a fish tank faster, you need to add MORE beneficial bacteria. Bacteria increase in numbers at a fixed rate. So, the more beneficial bacteria you add the faster their numbers will increase!

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