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The nitrogen cycle is a natural cycle where beneficial bacteria breaks down toxic compounds into less toxic versions helping protect our livestock from their own waster. Each time one of these compounds is processed into another form (from ammonia to nitrites), they are made less toxic. The three compounds we see in aquariums are Ammonia, Nitrites and Nitrates. Ammonia which is generated by fish waste is far more toxic at only .2ppm, where nitrates (the end of the cycle) can get into the 200ppms before we see effects on our livestock. Understanding that ammonia is EXTREMELY toxic to livestock we NEVER want to put fish in prior to having this natural beneficial bacteria in our aquariums as it is cruel! In order to encourage these beneficial bacteria to grow, we need to start the cycle off with ammonia. After the tank has cycled for 4-8 weeks, this beneficial bacterial will help keep your fish safe from organic waste in your tank.  

Cycling a tank is quite easy and often takes more patience than work. The start of this cycle is ammonia. Ammonia is introduced into the tank. This can be from decaying organics like fish food, household ammonia, or even aquasoils that leach lots of ammonia. Aquasoils that do this are presented as a bad thing, but I see it as a free way to start out your cycle. The presence of ammonia causes natural beneficial bacteria to colonize. They thrive from breaking down the ammonia into nitrites. Now with the presence of nitrites, another form of a natural beneficial bacteria ends up colonizing, breaking down the nitrites in nitrates, and that is the end of the cycle. However, there is no bacteria that breaks down nitrates thus forcing us to process water changes to remove them.

How to cycle a tank without fish

We can start a cycle in a few different ways. One way is by introducing normal household ammonia daily. There are special products one can buy like Dr. Tims Aquatic Ammonia, or you can use basic household ammonia. You’ll add a few drops per day till your tanks ammonia level reached around 3ppm, not to exceed 5ppm. Remember that .2ppms of ammonia is toxic to livestock so please do not begin this processing with livestock in your tank. The ammonia feeds the first type of bacteria stimulating the chain reaction of beneficial bacterial growth in our filters biomedia. Another way to cycle your tank is by using an aquasoil with high organics, like ADA Amazonia. The aquasoil will naturally release ammonia into the tank stimulating your cycle. However, high organics aquasoils can leach ammonia for weeks causing you to have to be more patient. Tanks with ADA aquasoils can take up to 6-8 weeks to cycle.


  • Household Ammonia

  • Dr. Tims Ammonia

  • ADA Aquasoil

  • Seachem Stability

(Links below)

Things that can help speed up a cycle

There are products and/or processes that you can do to help speed the cycle up. As far as products go, there are bacteria cultures in a bottle that you can add to a brand new tank to help kickstart the amount of beneficial bacteria in the tank. This doesn’t feed the bacteria, but simply adds good bacteria to the tank to help get it started. Seachem Stability is a good example of this. We can also take biomedia (ceramic rings) from an established tank and put them into our filter. Your local fish store might even have bags of cycled media for sale. Again, this does not instantly cycle out tank, but helps the process along. We still need to verify that the ammonia and nitrites in the tank are being converted in nitrates. We’ll talk about how to know the cycle is complete later.

What to avoid

Again, avoid using your fish and their waste as an ammonia source. You’ll also want to avoid processing water changes or using chemicals that can remove/neutralize the ammonia, like Seachem Prime, as the beneficial bacteria need ammonia and nitrites to get their colonies going in your filter and substrate. Removing ammonia or nitrites just takes away their food source during the cycle.

What can we expect while cycling a tank

For the most part, not much will happen visually, and this is what causes aquarists to become inpatient. If you have plants, they will be more than happy to help soak up some of the extra ammonia and nitrites causing a growth spurt. When cycling with an aquasoil like ADA, the water might get cloudy or milky. This will have a white color, not green, hazy color. The green-sih colored water is an algae bloom which is another issue. As long as your water is white and hazy, you just need to continue to be patient. This is just a visual indication of ammonia present in the water column.


How do I know when the cycle is complete? You will need a test kit, or access to one at your local fish store. API sells individual ammonia, nitrite, and nitrate liquid test kits. I’ve used them for years and love the product. Once you see that 1) there is no more ammonia or nitrites in the water, and 2) you have lots of nitrates in your tank, you know the bacteria is prevalent! Now, this doesn’t mean that you can go to your local fish store and toss in 100 fish into your 10-gallon aquarium. This means that you’ve started the bacteria and you’ll need to go slow with adding livestock that will create more ammonia in the tank. So only add larger fish in a couple at a time, or a small schooling fish 5-6 at a time. Enjoy this process of adding a few fish, letting your bacteria catch up with the new bioload, then go add a few more till you are where you need to be.

What problems can arise

Some types of medicine, like ich treatment, will kill off beneficial bacteria. It is always suggested to treat fish in a hospital tank as to not upset the balance of your primary tank. If you toss medicine into your primary tank it can kill your good bacteria resulting in ammonia and nitrite levels increasing with the release of fish waste which can ultimately result in livestock deaths. One can also overwhelm our good bacteria which too many fish at at once, or over time. The amount of good bacteria we established in our filter can only consume so much ammonia and/or nitrites at any given time. If we toss too many fish in, the bacteria will increase over time to accommodate, but sensitive livestock could die prior to our bacteria catching up. So this is why we add a few fish in at a time, lets say every week to be safe. Furthermore, the size of filter and its flow dictates how much of the tanks ammonia and nitrites are brought to the bacteria for consumption. Yes, one can get away with a really low flow filter if their bioload is really low, as in they don’t have a lot of fish or organic waste. However, if you add too many fish into a tank with a low turnover filter, you can run into a situation where ammonia and nitrites build up in the tank and are not being sucked up and process by your filter. This is why I always suggest having a filter that can turn your tank over 10x an hour. I see a lot of fish deaths in forums and Facebook groups due to lack of filtration, or even biomedia in things like hang on back filters. Its generally not the filters fault and more just ignorance by the user, but a canister filter is generally always going to outperform a hang on back filter, and has less room for user error.

Related Produts

Cycling Products

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