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Can You Cycle a Fish Tank in 24 Hours? Fastest Way to Do It!

A large fish tank with lots of fish and other fish tank items with a blue light shining on it.

Cycling a fish tank is required for putting new fish into a tank. So, it means you need to wait around for it to be completely cycled, and for the nutrient levels to be in a range that is healthy for your fish. However, it’s very exciting to get new fish into a tank, so here’s whether it’s possible to cycle a fish tank in 24 hours.

As a general rule, it is possible to cycle a fish tank in 24 hours. To do it you need a water filter from an existing tank that is already cycled, and/or add the recommended dosage of Fritzyme 7 Live Bacteria (this live bacteria on Amazon is great value).

Usually, if you just put water into a fish tank it will take 4 to 5 weeks to cycle to produce enough beneficial bacteria so that your fish don’t suffer or die. It’s important to know where to get an existing fish tank filter if you don’t already have one.

So, below I will explain where to get one, and how it’s possible to cycle a fish tank in 24 hours.

How To Cycle a Fish Tank in 24 Hours

Now that you’re aware that it is possible to cycle a fish tank in 24 hours, it’s important to know how to do it. Below, is a summary and full instructions for how to cycle a fish tank in 24 hours.

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In general, you simply place a water filter from a tank that has already been cycled into your new fish tank. Within 24 hours it will be completely cycled. Adding sponges and items from an established fish tank can also be good to promote the growth of beneficial bacteria.

An existing water tank has a large number of beneficial bacteria, these bacteria grow all over the physical surfaces of the tank and are particularly concentrated in the water filter

So, putting a water filter from an established tank, or one that has been set up to cycle a new tank will cycle a fish tank much faster. Fish-keeping experts explain that if you put a water filter from an established tank it will cycle in about 24 hours.

Where To Get an Established Water Filter or Sponge

If you’re new to keeping fish, then you won’t already have a water filter that is cycled. Therefore, it can be a bit tricky to know where to get one

There are three places you can get a used water filter or sponge with a lot of bacteria in it:

  • a local fish-keeping club
  • friends or family that have fish tanks
  • your pet store

Fish-keeping is a really fun hobby, and there are almost always local groups of people who keep fish, and there are a lot of benefits to knowing people with aquariums. Many hobbyists will keep a whole room dedicated to fish tanks, and swap fish species with each other.

Experienced fish keepers are aware of the long amount of time it takes to cycle a fish tank. So, often they will have a few cycled filters as a backup. If you join a fishkeeping group, people are more than happy to help a new fishkeeper, and will gladly give you (or sell for very cheap) some cycled medium, like a pre-cycled water filter.

The next place you can find a pre-cycled water filter or sponge is with family or friends that also keep fish. A friend will typically be happy to give you the sponge that is currently in their water filter. Especially, if you say you will give them one back!

A fish tank with various fish, plants, and rocks.
A used sponge with plentiful bacteria is helpful

TOP TIP: People who have a lot of aquariums almost always have a pre-cycled water filter you can borrow to get your tank started.

Lastly, some pet stores (particularly those that specialize in fish) sometimes have some pre-cycle water filters or mediums, such as a sponge or sponge-like material.

Placing a Sponge in a New Water Tank From an Established Tank

Sponges are particularly good at holding bacteria. Placing them in the compartment of your water filter, or somewhere in your tank (out of sight if possible) will increase the levels of beneficial bacteria

A piece of sponge that has been placed in the water filter compartment or in the tank will have a large number of beneficial bacteria growing on it in about 1 month

Squeezing one of these sponges out into an established tank, and leaving it somewhere in the tank will speed up the time it takes to cycle a fish tank. It will also allow the fish tank to cycle at a fast enough rate once new fish are placed in it

Keeping a Close Eye on the Ammonia Levels

The main nutrients that you need to be aware of when cycling a fish tank are ammonia and nitrite.

FUN FACT: Ammonia is produced by fish and snails when they poop!

The ammonia levels take time to build up in a new fish tank. In a cycled fish tank there will already be a lot of beneficial bacteria that will break down the ammonia. However, in a new fish tank, this bacteria won’t be present, because it takes 4 to 7 weeks for beneficial bacteria to build up.

During this time the ammonia levels in the water will be too high for all species of fish. This has the effect of making the water acidic which can burn the fish. While they might not show outward signs of this happening, they will be in a weakened state, and it’s more likely they will:

  • get sick
  • get parasites
  • die

Before introducing fish into a new fish tank it’s important to have the levels of ammonia and nitrate in a safe range. Each type of fish has a unique level of ammonia and nitrate that they prefer. These are measured in parts per million, abbreviated as ppm.

Adding Fish – Do It Slowly

It’s recommended to get a good water testing kit, like this one from Amazon, and measure the levels of:

  • ammonia
  • nitrite
  • nitrate

You need to be sure these levels are not too high before adding your new fish to the tank. However, when you add fish you should also do so slowly because each fish produces ammonia

Ammonia will build up faster the more fish there are, and the beneficial bacteria can have a hard time breaking it all down. Until the beneficial bacteria levels are very high, you should only add a few fish at once.

An empty fish tank with only rocks, a filter, and one plant.
Only add a few fish at a time so the bacteria and ammonia levels can balance out

NOTE: Adding new fish to the tank slowly will give the bacteria enough time to break down the ammonia until the levels of bacteria have increased enough to handle more fish.

How To Know If Your Tank Is Cycled

A cycled tank is one where there are ample amounts of beneficial bacteria to handle the amount of ammonia put into the water tank by fish. Bacteria are often not visible to the naked eye, so it’s hard to know what the levels are and if they’re high enough.

Here’s how to tell if your fish tank has been cycled:

Use a water testing kit (like this one from Amazon) that can test the levels of:

  • ammonia
  • nitrite
  • nitrate

They should be at healthy levels for the specific species of fish. Also, spikes in the levels of any of these should not go above healthy levels.

Each species of fish is different and requires different maximum levels of:

  • ammonia
  • nitrite
  • nitrate
  • pH

Refer to the various care guides for your specific species of fish online to see what the maximum levels should be to keep them healthy and happy. 

If you notice your fish are sick or weakened, it is a sure sign the levels of ammonia, nitrate, and nitrate, are too high. For this reason, it’s a good idea to have a backup tank that is already established when possible. 

NOTE: When you have an established backup tank, you can take the fish out of the existing tank until you identify what’s causing the issues, and return it back to a healthy state for your fish.

How Long Does It Take To Cycle a Fish Tank?

Cycling a fish tank is required before putting fish into a new fish tank. Otherwise, ammonia and nitrite levels will get too high and can damage or kill them. But, how long does it take for a fish tank to cycle completely?

It usually takes 5 to 7 weeks to cycle a fish tank if nothing is added to the water. However, if a water filter from an established tank is added to a new fish tank it can take as little as 24 hours to cycle a fish tank. The limiting factor is the number of beneficial bacteria in the tank.

To decrease the time it takes to fully cycle a tank by half, add items from an established tank such as:

  • substrate
  • rocks
  • plants

Then the process would only take 3 to 4 weeks.

There are also specialist liquids that add beneficial bacteria to the water. However, fish-keeping experts are of the opinion that virtually all of them are ineffective. But, they do recommend a specific one called Fritzyme 7 that contains live bacteria in it (you can purchase it here on Amazon). 

Unlike other liquids that claim to help with cycling a fish tank the liquid in Fritzyme 7 actually looks alive. It also has an expiry date that it needs to be used otherwise the live bacteria will die.

Do You Have To Wait 24 Hours To Put Fish in a Tank?

Before putting fish in a tank, the tank needs to be at the right temperature for the type of fish. Unfortunately, it also needs to be cycled which can take a very long time. It’s common for new fish owners to not be aware of these factors, but here’s whether you absolutely must wait 24 hours before putting fish in a tank.

In general, you do not need to wait 24 hours to put fish in a tank. Provided the fish tank is cycled, fish can be put into it straight away. However, it’s a good idea to only add a few fish at a time. This will allow beneficial bacteria to keep up with the added ammonia in the water.

A fish tank with with fish, rocks, and a plant.
Pre-cycling a fish tank is the best way to have healthy and happy fish

If you put too many fish in a tank at once, it can cause a large amount of ammonia to enter the water. This occurs because the amount of ammonia that is entering the water is too much for the beneficial bacteria to break down. 

Especially when the amount of beneficial bacteria in the water isn’t very high. For example, in a new-ish fish tank. Once a fish tank is 2 months or more old, it will have more than enough beneficial bacteria to handle any amount of fish

This will overwhelm the number of beneficial bacteria in the water. However, if you add a few fish, the beneficial bacteria numbers can easily recover, and continue to break down the ammonia.

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