5 Proven Methods For Cycling A Fish Tank: Which One Is Fastest?

In Tank Cyclingby PaulK

Does this sound like you?

You got a new fish tank.

You set it up but then…

You’ve heard that you have to cycle the tank first before you add the fish.

What? I have to wait several weeks?

Cycling a new fish tank can take up to several weeks, but there is one way to do it faster. Proper fish tank cycling means getting enough good bacteria in your filter media to absorb the bad ammonia and nitrites that fish waste and other waste produces. Once your water reads at 0 ammonia and 0 nitrites, you are good to go. Nitrates are also present but in small amounts are not harmful to tropical fish. If you have live plants, that should take care of it.

I’m going to cover 5 common methods to cycle your fish tank and the pros and cons of each.

Let’s dive in….

Fishless Tank Cycling

This is the fastest and best way to cycle a new freshwater fish tank if you don’t have established media. You can cycle a tank in about 7 days.

First, you’ll need a good test kit like this API master test kit on Amazon. It accurately monitors the 5 most vital water parameters in your freshwater aquarium. Ammonia, nitrites, nitrates, pH, and hardness.

  1. Once your tank is full and ready to go with a substrate, plants, and aeration, turn on and run your filter, then add some live nitrifying bacteria starter to get bacteria growing in the media. Adding this will cut the time to cycle by about 2/3. Check the expiration date and make sure it’s not expired.
  2. Then add some ammonia chloride. This will seed the bacteria growth. You must use the live nitrifying bacteria with the ammonia chloride in order to see results.
  3. Test your water every few days. The ammonia level shouldn’t go over 3 ppm. I have an article on how to test your water if you need it.
  4. The water should cycle within a week and should be safe after that time. Test the water to be sure. When you start to see nitrites rise, you’ll know the cycle has started. Continue to add ammonia. Eventually, beneficial bacteria will start to grow and you will have a drop in nitrites and a rise in nitrates. At this point, the cycle is near completion.
  5. Introduce the fish when ammonia and nitrite levels are zero.
  6. Change the water frequently, like every other day at first. If you use tap water, you will have to treat the water first to get rid of the chlorine. Use something like Seachem Prime. If you don’t, it will start to kill all the good bacteria you’ve built up and create ammonia/nitrite spikes. Then you’ll have to start over.
  7. Continue testing the water until you are at a safe level and you won’t have to change the water quite so often. Just every week or so.

Cycling a New Tank with Fish

You have to be very cautious with this method.

  1. If you are going to go this route make sure you have a hardy type of tropical fish that can handle changes in water parameters. A few good choices are zebra danios, tiger barbs, most guppies, minnows, and tetras. It’s better to start with a few small fish in a big tank.
  2. You’ll want to get some already established bio media from another fish tank. You shouldn’t try this with new bio media.
  3. Do not add ammonia!
  4. Underfeed your fish like maybe once every other day.
  5. Do frequent water changes like 20-25% every few days. Don’t use chlorinated water as this will kill the new bacteria. Use a de-chlorinator like Seachem Prime. If you see signs of stress like fish gasping for air at the surface or lack of movement, then you’ll want to do more frequent water changes. Also, add an ammonia neutralizer if you see ammonia spikes.
  6. Test the water every day. I recommend getting a good test kit for this. Ideally, you want the ammonia level below 0.5mg/L and nitrites below 1mg/L. If you see spikes, then do a water change.
  7. Once the ammonia and nitrite levels are at zero, you can start to add more fish. Don’t add too many. Just slowly add a few more at a time.

Cycling a New Tank With Goldfish

Use goldfish only for a goldfish tank.

  1. Do a fish-less cycle and then add one or two goldfish at a time a week or two apart. Another option is to have a large aquarium with one goldfish, feed it sparingly, and do 20% water changes every couple of days. Lots of live plants will reduce any stress on fish during a fish-in-tank cycle. 
  2. Cycling a tank with goldfish and then adjusting the tank to accommodate tropical fish can cause at least some of the bacteria to die from the higher heat and different water conditions. This stresses the goldfish, the bacteria, and the tropical fish — not a recipe for a healthy tank.
  3. Don’t cycle with feeder goldfish. Feeder goldfish are more susceptible to disease.
  4. Don’t use chlorinated water. The chlorination kills bacteria which you need to feed on the toxins. If you use tap water, use a de-chlorinator before adding to the tank.
  5. It’s also a good idea to underfeed them rather than overfeed them since the less waste produced the better.
  6. If at all possible, get a used filter media with bacteria already in it. This will help cycle the tank faster.
  7. Use a conditioner like Seachem Prime. It will detoxify, but not remove the ammonia.
  8. Once ammonia and nitrate levels are near zero, you can start to introduce more fish. Gradually introduce more fish and continue to test the water every week or so.

Cycling a Fish Tank with Fish Food

This method is the slowest way because it takes a long time to get the cycle going. Also, you could potentially be adding phosphates to the new tank which spur algae growth.

  1. You can do this with regular fish food or raw, uncooked shrimp. Fish flakes break down faster than pellets. If you use uncooked shrimp, you need to chop into small pieces first.
  2. You should see ammonia build up first, then the ammonia will go down and you will start to see nitrites build up. Once the nitrite level goes down, you should start to see nitrates build up. This process can take several weeks so you need some patience.
  3. Keep testing the water every few days to see where you are in the cycling process.
  4. When the ammonia and nitrite levels are down to near zero the tank is ready.

Fast Tank Cycling

  • Use filter media from another established tank. There should already be beneficial bacteria in the filter media to eat the ammonia and nitrites.
  • Use substrate gravel from another established tank. Just take a few scoops and add it to the top of your current substrate. Not as effective as used filter media.
  • Use live plants. Live plants also help absorb harmful chemicals. Fast growing plants like Vallisneria or Hygrophila absorb the most ammonia.

Common Problems With Tank Cycling

Ammonia stress and new tank syndrome. If the level of ammonia gets too high to where it’s at a toxic level for fish, you’ll need to change the water. Consider using an ammonia neutralizer if levels get too high.

If you are using media or substrate from another tank, you run the risk of introducing algae and/or parasites into the new tank.

If you are cycling with fish in the tank, it’s better to be safe than sorry. Be overly cautious. Monitor the ammonia and nitrate levels constantly. Don’t overfeed the fish and only start with a few fish. Use additives in the water to make it less toxic. 


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How I Cycle My Fish Tank Like a Pro

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When it comes to fishkeeping, what is your single biggest challenge or frustration? Leave a comment below.

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