5 Tips for the Fastest Fish Tank Cycling

Fish tank cycling can be a slow (and painful for some :P) process.  It might take up to 6~8 weeks to finish.  In the case of fishless cycling, some people might become impatient.  They just can’t wait to get their fish. There are certain things we can do to finish the aquarium nitrogen cycle a lot faster.

Reason for the slow Fish Tank Cycling

All the new fish tanks start with near zero beneficial bacteria of both types.  (Nitrosomonas for converting ammonia, and Nitrobacter for converting nitrite).  It takes time for them to multiply to a level where they can make an impact on the ammonia and nitrite.

More importantly, Nitrobacter will not even start to grow in number at all until there is nitrite in the water. For nitrite to appear, there must be enough Nitrosomonas to feed on and convert ammonia first. It can take 2~3 weeks before Nitrosomonas grow into sufficient number to provide nitrite for Nitrobacter.  It is a bottleneck right there to slow everything down.

We should make both stages starting simultaneously from the beginning.  The whole aquarium cycling can be a lot faster.

Three Tips to Speed up Fish Tank Cycling

1. A good filter
2. Heavy bacteria seeding
3. Higher water temperature
4. Higher oxygen level
5. Keep nitrate low

A Good Aquarium Filter

Since most of the aquarium nitrogen cycle bacteria reside on the filter media, it is essential to have a good aquarium filter.  A good filter means it not only has plenty of filter media for massive bacteria colony, but it also has high water flow rate.  Canister filters have the most filter media, and it is highly efficient for biological filtration.

Whatever filter system you choose for your aquarium, get one that is rated higher than your fish tank size is also a good idea.  The higher size fish tank the filter is rated for, the more filter media and more flow rate it has.  You can never have too much filtration in a fish tank.

Heavy Bacteria Seeding

To have some beneficial bacteria to start the aquarium nitrogen cycle will undoubtedly speed up the fish tank cycling. More importantly, to have both Nitrosomonas and Nitrobacter to begin the cycle from the very beginning can be a tremendous jump start.  Because it eliminates the waiting period for nitrite to appear.

Media from well-established aquariums

Traditionally people seed bacteria by using something from an already established aquarium. It can be a decoration or some gravel. The best thing to use in this case is a piece of filter media. Most of the beneficial bacteria colonize the filter media. By placing a piece of filter media from a well-established aquarium into a new filter, you can give quite a jump start to the aquarium nitrogen cycle.  Since not everyone has access to a well-established aquarium, this form of bacteria seeding might not be available.

Bacteria in a bottle

Nowadays, there are commercially available bacteria seeding products.  They are great for the jump-start the aquarium nitrogen cycle in new aquariums if you are willing to spend a little extra money.

There were some old bogus products with incorrect species of land-based bacteria in them. When you use those bogus products in an aquarium, at first the tank might seem to be cycled quickly.  But it will not last.  Because the land-based bacteria will drown in the water eventually. The result is the user must keep dosing those products to keep the aquarium nitrogen cycle from crashing. Due to the widespread of such bogus products in the past, many people believe all bacteria seeding products wouldn’t work. This is a misconception and old news.

Dr. Tim identified the correct species of bacteria and came up with a way to store them in a bottle in liquid form.  The first proven working product was Bio-Spira. It was not long before Tetra re-branded the same product into Tetra SafeStart which was more widely available and many aquarium hobbyists have successfully used it to quickly cycled their aquariums. The very same product is now in even more different bottles with different names. Dr. Tim’s One and Only is just another example.

These commercially available bottled bacteria are all proven working after tried by many fish keepers.  They are meant for the cycle with fish because most people are not patient enough to do the fishless cycling in an empty fish tank.

I have personally used Tetra SafeStart twice for the fishless cycling with pure ammonia on two occasions. In one case, it cycled my fish tank in just one week.  In the other case, it cycled the fish tank just 24 hours after the dosage.  It was amazing.  In both cases, the fish tank was cycled permanently.  Both ammonia and nitrite were 0ppm with an increasing amount of nitrate.

There were plenty of good reviews from other fish hobbyists before I even tried Tetra SafeStart.  The good results were no surprise to me.

When you use a commercial bacteria product, make sure you get a bottle that is rated higher than your fish tank.  The bigger the bottle, the more bacteria it has.  A lot of these products require the user to shake the bottle extensively before using.  Make sure you do not skip this step.  You must also dose the entire bottle in one go since the product will start to expire after you opened the seal.

Higher Water Temperature

Like most bacteria, both Nitrosomonas and Nitrobacter love warm water. In the case of fishless cycling, you may turn the aquarium heater up and raise the water temperature to be middle or high 80F.  It will speed up the multiplying of the beneficial bacteria. High temperature can also increase their appetite for ammonia and nitrite. Although it will not make the day and night difference in the total time required, it will certainly shorten it to some degree. Every little help counts when you can’t wait to get your hands on the new fish, right? 😛

Higher dissolved oxygen level

Both Nitrosomonas and Nitrobacter require oxygen to multiplying. A rich oxygen environment will undoubtedly help them grow faster.  Therefore, it shortens the fish tank cycling time. You can quickly achieve this by turn up the aquarium air pump and add more air stones. It is also required if you use higher temperature from the previous tip.   The warmer water holds less oxygen.

Keep Nitrate Low

The production of nitrate is acidic.  As more nitrate appears, it slowly eats away at the water buffer.  You might see the water PH slowly drop.  Once the water buffer is all gone, then there will be a sudden PH crash.  You might see the water PH go from 7 to 5 or even lower in one day.  When it happens, the acidic environment is not ideal for bacteria growth.  The fish tank cycling might be slowed or even stalled.  Do a partial water change to reduce nitrate concentration, and to restore water buffer at the same time is beneficial.

You only need to do the partial water change when there is excessive nitrate.  Partial water change too early will reduce ammonia and nitrite, which is not a good idea.


There is no set time for how long it will take to cycling fish tanks.  Each case may vary due to unpredictable variables.  Even when you use a live bacteria product for heavy seeding, it could be different every time.  Each bottle might give different results due to the way the product was transported, handled, and stored.  It affects the bacteria concentration in the product.

By applying all of the tips to speed up aquarium nitrogen cycle, you will at the very least be able to get the fastest results you can get.

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18 thoughts on “5 Tips for the Fastest Fish Tank Cycling

  1. Max

    If i pull half water out of my 55 gallon freshwater tank to jump start my cycle, how long before I can add fish

    1. Thor Post author

      Did you actually use any source of ammonia and live bacteria product? If not. It will take minimal 4~6 weeks for the fishless cycling to finish. If you did both, it might take a few days to a week. To be sure, you need a test kit to check on ammonia and nitrite levels.

      Water does not hold the beneficial bacteria. They reside on the surface area of underwater objects. The one thing with the most surface area is the filter media.

      1. Lyuba

        Hi! I was wondering if you were adding a little bit of bacteria every day (Safe start) or the whole bottle one time? Please, let me know ! Thanks!

        1. Thor Post author

          Hi Lyuba,
          You need to dump the whole bottle of Tetra SafeStart into your fish tank at once. After you have set everything up with filter running of course.
          The live bacteria in the bottle will not last long once you have opened the seal. So you have to use it all at once.

    2. Sam

      None. Because beneficial bacteria does not live in the water. They live in most surfaces like your substrate, filter media and the glass of your tank. So pulling water does not help in any way.

      1. Aaron

        No putting water in won’t help the nitrogen cycle but if you where impatient and want fish in fast. Using water from an established tank will jump start the heating process! 😛 It will also help with PH levels in your tank.

        1. Thor Post author

          Water does not hold the beneficial bacteria required for the nitrogen cycle. These bacteria colonize the surface area of underwater objects. So moving the water from an old established aquarium won’t help. The best thing you can get is a piece of filter media from an established aquarium, or a bottle of live bacteria such as Tetra SafeStart.

          PH is not too much of a concern if you acclimate the fish and give them time to adapt.

  2. nayana

    I’m on day 10 of doing a fish less cycle on a ten gallon tank that will be split for two bettas. I’m using fish food as my ammonia and it’s at 0.50 ppm. There are no nitrites yet. I added an air stone today and the water temp is at 78 degrees. Should I buy the tetra safe start to speed my cycle?

    1. Thor Post author

      What filter are you using? If you have a sufficient filter, then sure, Tetra SafeStart will help. You should immediately see nitrite and nitrate 24 hours after you have used this product.

  3. Kaelee McCoy

    Nayana you need to add more fish food for ammonia if the ammonia is so low and there isn’t any nitrites you need more ammonia

  4. Laurali

    Ok i just started my 60 gallon hexagon wet dry filter my 20 gal filter just broke on me 1st day of cycling my bigger tank. Im putting logs, plant mesh and some old fish food plus what ever else gets left on the gravel. Filter i threw away not knowing i could use it. How long eill it take to cycle? I have 10 fish in my 20 gal that i need to transfer over to the 60 gal. Whats the soonest i can do that because they have no filter?

    1. Thor Post author

      Hi Laurali,
      It will take 4~6 weeks for the filter media to be cycled if without heavy seeding from either live bacteria products or some filter media from your old fish tank.

  5. KK

    Hi, I’m starting week 2 cycling. So far, low ammonia levels but the pH and nitrite levels are off the charts while the nitrates are at 10 ppm and ammonia is at 0.500. I added bacteria, old tank water, moss balls, a bubbler and fish food to get it ready. Should I replace water or do anything else? Is the low ammonia level good or bad? I’m so lost lol thanks for the help!

    1. Thor Post author

      Hi KK,
      As long as the PH isn’t as low as below 5~6, you are fine. When PH is too low, it stalls the bacteria growth because they do not like acidic environment.

      You are doing great. Just two weeks in, you already have both nitrite and nitrate. You are making good progress. My first fishless cycling too more than that to just see the nitrite.

  6. Melanie

    I already have fish in my tank, we have had it up for about a year, but we got a bigger filter and put the new one one the tank and took the old one off, but we did not put the old filterationg in the canister, so with it being brand new fliters on our tank it thru everything off balance, we have done a 50% water change but its still out of wack been this way for almost a week now, were affraid our fish will die. What can we do to get everything back on track. Please help.

    1. Thor Post author

      Hi Melanie,
      You could have used the old filter to run along side the new filter until the new filter is fulled cycled.

      If your old filter was taken out and dried for more than a few minutes, then the bacteria in there must have died. But you still can use two filters at the same time to make the cycling go quicker.

      Meanwhile, what you can do is to use SeaChem Prime to do partial water changes every day or so to keep the toxic at minimal until the new filter is cycled. You can also get a bottle of Tetra SafeStart, the biggest bottle you can fine. Then dump it all into your fish tank at once. It will get the cycling process to speed up by 10x over.

    1. Thor Post author

      Fish food creates ammonia when it rots. So you have a source of ammonia. Yes, a source of ammonia is required to get cycling process started.

      Do you have a good filter? A good filter will cycle faster as well.


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