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Humane Cycling Kate Redman

Often, the chosen method of introducing ammonia products to a newly set up tank, thereby allowing the nitrogen cycle to begin, is by introducing one or more hardy fish to the tank. The fish’s role is to consume food and to excrete nitrogenous waste products, which break down into ammonia, a substance that is highly toxic to fish. In turn, the ammonia attracts nitrifying bacteria, naturally present in the atmosphere, which breaks it down into less-harmful nitrogen compounds. Once nitrifying bacteria is resident in the tank, and the ammonia is being cycled out (and as long as all other water parameters have been met) the main fish species can be slowly acclimatised to the aquarium. Failure to carry out the nitrogen cycle can lead to “new tank syndrome”, a situation whereby ammonia levels have reached highly stressful, or toxic, levels [1], which could ultimately kill your fish.


Hardy fish are less susceptible to the initial high ammonia levels caused by the build-up of waste products, which is why they are commonly used to trigger the nitrogen cycle. Species used can depend on the tank you’re setting up [2], but examples include [3]:


White cloud mountain minnows (Tanichthys albonubes)

Zebra danios (Danio rerio)

Cherry/Tiger barbs (Puntius titteya/Puntigrus tetrazona)

Zebra mbunas (Maylandia zebra, aka Pseudotropheus Zebra)

Banded gouramis (Trichogaster fasciata)

X-ray tetras (Pristella maxillaris)

Pupfish (approximately 120spp within the family Cyprinodontidae)

Most minnows (family Cyprinidae) and guppies (family Poeciliidae)


Nevertheless, despite these fish species being considered hardy, exposing them to a toxic environment is still putting these animals under unnecessary stress. Further, should the cycling not work, these fish could well end up dying for nothing, and if the cycling does work, there remains the question of what to do with the fish. Do you keep them with your main fish? In which case, are they a suitable species to house alongside them? And if not, what will become of them? Something else to consider when using hardy fish is that they may well introduce unwanted pathogens to your new aquarium.


Issues such as those above is why ‘humane cycling’, or ‘fishless cycling’, is a better way to go. It involves no fish, but the result is the same, namely an aquarium that contains nitrifying bacteria that can cycle out ammonia. The method involves adding a non-live fish source of ammonia, with the option of speeding up the process by adding sources of nitrifying bacteria [4].


Ammonia can be introduced to your tank in a number of ways [4]. One method is to use already decaying matter, such as a raw prawn, or fish food. Another, slightly more precise method, is to use bottled ammonia of the type used for household cleaning (bear in mind, this is not the same thing as bleach!), and that can be purchased from some chemists or hardware stores. Small amounts of the liquid ammonia can then be fed daily to the bacteria using a pipette. But make sure it’s pure ammonia, free from additives like foaming agents or perfumes, and be careful when handling it. Lastly, you can use human urine, as it too contains ammonia, and it too can be pipetted into the aquarium, just like the bottled ammonia. Still, it’s probably better (read: nicer) to go the fish food route.


To make sure the cycle can take hold, ammonia levels need to be kept at least 3ppm [3]. As the nitrifying bacteria take hold, they will start to consume the ammonia, reducing its levels, so test the ammonia levels of your tank water every other day, and should it dip below 3ppm, add more ammonia. Then, after about a week, begin testing for nitrites. Nitrites are the intermediate chemical in the nitrogen cycle, and once you detect them, you'll know the cycle has started. However, nitrites are still toxic to fish, so it’s still not the time to add them to the tank. Rather, keep adding ammonia to the tank to feed the process. The nitrite levels will continue to rise, but eventually enough nitrifying bacteria will be present to convert these nitrites into nitrates, the final chemical in the nitrogen cycle, and the one that isn't harmful to fish. Depending on what water chemical testing you’re doing, you’ll either see a sudden drop in nitrates, or a sudden spike (from a base level of zero) in nitrates, or both. Once the ammonia and nitrite levels are so low as to be undetectable, and the nitrate levels have plateaued, so long as all other environmental parameters are met (salinity, temperature, etc.) it is safe to begin acclimatising your fish to the water.


Although humane, this process of cycling an aquarium can take several weeks, which is why some people choose to kick-start the process by introducing sources of established nitrifying bacteria. There are a number of ways of doing this, though care is advised. One option is to introduce the substrate or filter media from an already established tank [3]. Either transplant a few scoops of substrate from a mature tank into your new tank, or switch the filter media from the mature tank to the new tank. This method reduces the time it takes for the bacteria to naturally colonise your new tank, but there are problems associated with doing this. First off, introducing substrate from another tank can also introduce unwanted pathogens and parasites to your new tank [3]. Secondly, removing substrate from a mature tank could unwittingly cause a mini-cycle in the donor aquarium, whereby the remaining bacteria are insufficient for the waste produced by the fish present [4]. It will then take time for the bacteria to multiply back to coping levels, and will put the fish in the donor aquarium under unnecessary stress. Alternatively, a pinch of soil from an organic garden will contain nitrifying bacteria [4] that may help to initiate the cycle. Unsurprisingly, the emphasis here is on ‘organic’, as you don’t want to add any residual pesticides to your aquarium.


Living plants can also help speed up the process, especially if introduced from a mature tank [3]. Not only can plants carry nitrifying bacteria on their surface, but they also pull ammonia out of the water directly via protein synthesis. Depending on the aquarium you’re creating (i.e., tropical, freshwater, etc.), fast-growing plant varieties like Vallisneria and Hygrophila work well, as do floating plants such as Amazon frogbit (Limnobium laevigatum) and Indian fern (Ceratopteris thalictroides) [5]. Keep in mind though, as with the substrate, the transplanting of plants from one tank to another could cause the transfer of unwanted parasites, invertebrates, and pathogens.


A further possible source of nitrifying bacteria is bacteria-in-a-bottle. However, you need to ensure what you’re buying contains the correct nitrifying bacterium, as in the past, this hasn’t always been the case [4, 6], and these products have been less than useful. Even today, there’s no guarantee that what you’re buying is useful bacteria, even if the bottle says otherwise [7]. That being said, there are some good products on the market now, and a lot of public aquariums use these due to time constraints in getting tanks set up [personal communique], so this is a good option. At present, several specific types of nitrifying bacteria have been linked to ammonia break-down in aquaria, including Nitrosomonas europaea [8] and Nitrospira moscoviensis/Nitrospira marina-like bacteria [9, 10]. So keep your eye out for these being listed on the bottle.


As well as introducing bacteria to the tank, another possible way to help the cycle is by turning up the temperature. Ordinarily, such a method would not be practical if fish were present in the tank, even tropicals, but there is some anecdotal evidence that suggests increasing the tank’s temperature reduces the overall cycling time [6]. This is because, under optimal conditions, bacteria can grow and divide extremely quickly, allowing bacterial populations to increase rapidly. Nitrosomonas europea prefers a temperature between 20-30oC [11], and Nitrospira-like bacteria do best between 28-30°C [12]. As such, increasing the aquarium’s water temperature to around 30oC could help the bacterium colonise the tank faster. But remember to slowly return the temperature to the tank’s correct temperature afterwards, otherwise any rapid change in temperature will kill the bacteria, undoing all your hard work. Also, if you’ve already placed plant life in the tank, depending on the species (e.g. cold-water loving plants), this method could cause them to die. So if you do employ this method, it’s best to do it independently of the plant-adding method mentioned above, and wait till after the cycle has completed before stocking your tank with plants.


[1] Beginner FAQ: The Nitrogen Cycle, and “New Tank Syndrome” (http://fins.actwin.com/mirror/begin-cycling.html) Accessed 27-August-2016


[2] Tips for Cycling Your New Aquarium (http://www.firsttankguide.net/cycle.php) Accessed 27-August-2016


[3] How to Cycle a Fish Tank (http://www.wikihow.com/Cycle-a-Fish-Tank) Accessed 27-August-2016


[4] Cycling an Aquarium (http://www.seriouslyfish.com/cycling-an-aquarium/) Accessed 27-August-2016


[5] Freshwater Aquarium Cycling (http://www.fishchannel.com/freshwater-aquariums/aquarium-care/cycling.aspx) Accessed 27-August-2016


[6] Koga J.S. (1996). Use Household Ammonia to Humanely Cycle a Tank. Freshwater and Marine Aquarium, 19(4), 213-214. Updated! (http://www.cpp.edu/~jskoga/Aquariums/Ammonia.html) Accessed 27-August-2016


[7] Nitrifying Bacteria Mixtures Work – Provided…. (http://www.drtimsaquatics.com/nitrifying-bacteria-mixtures-work-provided) Accessed 31-August-2016


[8]  Hovanec T.A., & DeLong E.F. (1996). Comparative Analysis of Nitrifying Bacteria Associated with Freshwater and Marine Aquaria. Applied and Environmental Microbiology, 62(8), 2888-2896. (http://www.drtimsaquatics.com/wp-content/files/scientificpapers/Hovanec_DelongAEM_Aug96.pdf)


[9] Hovanec T.A., Taylor T.T., Blakis A., & DeLong E.F. (1998) Nitrospira-Like Bacteria Associated with Nitrite Oxidation in Freshwater Aquaria. Applied and Environmental Microbiology, 64(1), 258-264. (http://www.drtimsaquatics.com/wp-content/files/scientificpapers/hovanecAEM_Jan98.pdf)


[10] Burrell P.C., Phalen C.M., & Hovanec T.A. (2001) Identification of Bacteria Responsible for Ammonia Oxidation in Freshwater Aquaria. Applied and Environmental Microbiology, 67(12), 5791-5800. (http://www.drtimsaquatics.com/wp-content/files/scientificpapers/hovanecAEM_Dec01.pdf)


[11] Nitrosomonas europaea (https://en.wikipedia.org/wiki/Nitrosomonas_europaea) Accessed 29-August-2016


[12] Off S., Alawi M., & Spieck E. (2010). Enrichment and Physiological Characterization of a Novel Nitrospira-Like Bacterium Obtained from a Marine Sponge. Applied and Environmental Microbiology, 76(14), 4640-4646. (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2901753/