What is fishless cycling?
This article is all about the relatively new technique of fishless cycling. This is intended to help fish keepers avoid what is generally known as New Tank Syndrome. As the name implies it is only applicable to new tanks that have recently been stocked with fish.. The technique of fishless cycling is designed to mature a biological filter in the absence of fish. This maturation process refers to the development of a healthy population of a well-balanced mix of bacteria, and other micro organisms. By so doing when fish are eventually added, once the fishless cycle is complete, the filter is immediately capable of purifying the resultant fish waste. A biological filter is widely accepted as the best method of controlling harmful wastes produced by fish. If allowed to accumulate, these substances would poison and eventually kill the fish.
The role of the Nitrogen Cycle
Nitrogen is the most abundant element on the planet, making up 78% of our atmosphere. It exists in many different forms by combining with oxygen and hydrogen, in particular, in a variety of combinations. The Nitrogen Cycle is an attempt to simplify the relationships between all these different compounds and shows, in a simplified diagrammatic way, how cycling occurs. In reality it is more of a web of relationships rather than the more commonly represented linear pattern as suggested by Cycle. It would be more accurately described as a collection of interconnecting cycles. This cycling is represented by a number of different processes, of which nitrification is the most important one as regards to fish keepers.
Nitrification – a two step process
Nitrification is a two step process, the first of which involves bacteria that are capable of converting ammonia into nitrite. This is important because ammonia is constantly being excreted via the gills of the fish and builds up in an aquarium if there is nothing there to consume it. Ammonia is acutely toxic to fish and most other aquatic creatures. Although nitrite is also toxic it is significantly less so than ammonia.
In reality ammonia is present in two distinct forms ammonia, NH3 and ammonium, NH4+. It is only the ammonia that is toxic. Ammonium is not. Unfortunately this causes great confusion with many fish keepers but it is essential to understand the difference between the two forms.
The proportion of each form varies primarily according to the temperature and the pH of the aquarium or pond. There are mathematical tables that show the percentage that exists as the toxic ammonia according to the pH and temperature. Without working out these values it is impossible to predict how badly fish will be affected . Notice that a rise in pH value of one, e.g. from pH 7 to pH 8 there is a tenfold increase in the amount of toxic ammonia present. High water temperatures will also increase toxicity significantly.
Generally speaking a water test kit will determine the Total Ammonia present. i.e. the combined amount of ammonia and ammonium.
When fish are added to a new tank there are not enough beneficial bacteria present to breakdown the ammonia that is constantly being produced by the fish. However ammonia oxidising bacteria (AOB) soon appear, as if by magic. They will utilise the ammonia to grow and increase in numbers. The ammonia level will consequentially decline once the rate of ammonia oxidation exceeds the rate that the fish are able to produce it. This inevitable leads to an increase in nitrite levels. This is the first step in the two step process of nitrification.
The second step of the cycling process involves another group of bacteria referred to as the nitrite oxidising bacteria (NOB). These are also beneficial bacteria as they convert the nitrite produced by the AOB and convert it into nitrate. Nitrate is considerably less toxic than nitrite and even more so than ammonia. Hence nitrification is the process by which toxic ammonia is converted into considerably less harmful nitrate. Once there is a sufficient population of AOB and NOB the ammonia and nitrite levels will remain low, or close to zero, and not harm our fish. Nitrate levels, in theory at least, will continue to rise. In reality they tend to flatten off as they can be reduced by
- denitrification using other bacteria that thrive in the absence of oxygen
- uptake of nitrate by algae and other plants.
- water changes.
Is Fishless Cycling necessary?
New tank syndrome is a very real threat to a new aquarium and must be correctly managed. Fishless cycling is a recent and popular method of controlling this threat, but it is not the only method. It has the advantage that it does not expose any fish to an elevated and potentially lethal level of ammonia and nitrite. Instead fishless cycling most often, uses a chemical, inorganic, form of pure ammonia to directly feed the bacteria that are so necessary to enable a bio filter to carry out its intended task. Organic sources of ammonia, most notably fish food, are sometimes used instead of, or as well as, liquid ammonia.
How to Cycle a fish tank using fish
Personally I prefer to manage the threat of New Tank Syndrome by using fish rather than the chemicals used during the fishless cycle. I do however, have the advantage that I have several fully mature fish systems that allows me to move fish around according to stock levels. For anyone without these facilities fishless cycling does offer an alternative, arguably more ethical, solution to the problem. I have found the following methods when using fish are both simple and effective.
- Stock initially with a minimal number of small fish when first setting up a new tank. 2- 3 individuals of the smallest available size is fine.
- Use a hardy species of fish such as goldfish, rather than your prize pair of breeding discus!
- Use a minimum amount of fish food. Feed by hand, no more than once or twice a day.
- Add a small amount of filter media from an established tank or aquarium to the new filter. This greatly speeds up the whole cycling process. Only use media from one of your own tanks to reduce the risk of introducing disease.
- Test for ammonia and nitrite at least every other day.
- If ammonia levels exceed 0.01mg/litre of free ammonia carry out a 50% water change.
- As an alternative to 6 above you could simply remove the fish until the ammonia level has returned to a safe level, preferably close to zero. Obviously if this is your first and only fish tank you will not have this option available to you.
- There are a number of bacterial preparations available that purport to speed up filter maturation both for fish and fishless cycles. I have never found these to be necessary and have doubts about many of their claims. I wouldn’t however discount them entirely.
How long does it take to cycle a fish tank?
The Golden Rule here is be guided by your water analysis rather than follow a set time frame. During a fishless cycle you should expect the ammonia level to start to fall after 4 -7 days. At the same time you are likely to see the nitrite level rise. It’s probably best to allow at least a month for the whole fishless cycling process to be complete. Providing pure ammonia as a food source, without any organic waste such as fish poo or fish food, will allow the AOB to increase without any competing heterotrophic bacteria. These grow much more rapidly than AOB and NOB and will slow down the population growth rate of the beneficial bacteria. The closer the aquarium water quality is to the optimum conditions for nitrifying bacteria the sooner the fishless cycle will be complete. Optimum conditions for nitrifying bacteria can be summarised as follows;
- Water temperature of 28°C – follow this link to find out more about fish tank temperature
- pH of 7.8 – follow this link for more advice about fish tank pH.
- High dissolved oxygen levels – follow this link for more advice about dissolved oxygen
- High surface area filter media. Nitrifiers prefer to attach themselves to a fixed surface and form a biofilm.
- Low levels of organic wastes. These wastes contain carbon that is an excellent energy source for heterotrophic bacteria. These are easily able to out grow the AOB and NOB and multiply much, much faster. Fish poo is the number one source of organic waste.
- Absence of light. Light has been shown to inhibit the growth of both AOB and, in particular, NOB.
How to Cycle a Fish Tank using pure ammonia
Cycling a fishless tank is relatively easy but you should allow sufficient time. 4 – 6 weeks is a good guideline. You will need a supply of household ammonia available from most hardware stores. Household ammonia typically contains 10% ammonia dissolved in water but this is not always the case and calculations to determine how much should be added may well need to be recalculated.
To carry out effective fishless cycling you will also need a number of water test kits. Ammonia and nitrite as a minimum, but pH and nitrate test kits would definitely be useful.
Some aquarists also like to use fish food as an organic source of ammonia. This probably generates more realistic populations of filter bacteria but be careful to keep quantities very low. Uneaten fish food will definitely encourage the more aggressive heterotrophic bacteria that can easily outcompete the beneficial bacteria that carry out nitrification. (AOB and NOB) They will also lower the level of dissolved oxygen of the tank water, possibly to a dangerous degree. A moderate population of heterotrophs will help the production of ammonia from organic materials though the process of ammonification. This should be in addition to nitrification by the AOB and NOB rather than a substitution and extra time needs to be allowed to complete the process.
The following fishless cycling technique is both simple and effective and the one I would recommend.
Step 1 – Set up and run the filtration system as normal
Set up the fish tank temperature and filtration system exactly as if there were fish present and run the circulating pump 24/7
Step 2 – Add a small amount of pure ammonia to the tank every day.
Add pure ammonia to the aquarium to raise the total ammonia (NH3 and NH4) to no more than 1 – 4 mg/litre over a period of a few days. Obviously you need to know how much ammonia to add to reach these levels. To more closely mimic a fish tank you should add ammonia at the rate of 0.5ml. of a 10% ammonia solution per 100 litres of tank water. This will give an initial concentration of ammonia of 0.5 mg/litre on the first day and reach 2.5 mg/litre after 5 days if no nitrification has occurred. Tank volume can be calculated by multipling the length by the width and the depth of the tank in centimetres and then dividing by 1000. So a 120cm x 60cm x 50cm would contain 360 litres and would require 1.8 ml. of a 10% ammonia solution to be added daily. This needn’t be too precise but avoid adding too much ammonia as this can inhibit the growth rate of the filter bacteria.
Step 3 – Monitor ammonia and nitrite levels closely.
After 3 days use an appropriate ammonia test kit to determine the current level. If the level is approaching zero you need to add more ammonia so move on to Step 4. If there has been little change leave the aquarium running for another couple of days and retest.
Step 4 – Continue dosing ammonia daily and monitor water quality
Add a repeat dose of ammonia daily and retest. By this time the nitrite levels should start to rises the fishless cycle kicks in. Confirm that this is happening by using a nitrite test kit. Leave the aquarium running for a further 2 – days and move on to Step 5
Step 5 – Introduce a small amount of fish food every day to encourage heterotrophic bacteria.
Carry out repeat, preferably daily, tests for both ammonia and nitrite. By this time the cycling process should be well underway. This will be shown by a decline in both ammonia and nitrite. To obtain further confirmation that nitrification is really happening you could now start to use a nitrate test kit. This parameter should now be increasing as the NOB are converting the nitrite into nitrate.
As an option you could also add a small amount of fish food. This will provide an organic ammonia source for other types of bacteria and arguably represents more accurately the type of conditions that will exist once fish have been added. Be cautious however and add only very small amounts of food. Add no more than about 20% of what you would add if fish were present. Personally I would avoid this option altogether. It will lead to a drop in a dissolved oxygen and potentially allow the bad bacteria to outcompete the beneficial nitrifying bacteria and is not an essential requirement for fishless cycling.
Carry out repeated water tests and every time the ammonia level approaches zero add some more.
Step 6 – Carry out partial water changes
Before adding any fish there is just one thing that could be done to optimise water quality and that is to carry out a final water change. The fishless cycle will have resulted in an elevated level of nitrate. Although this should not be harmful it is an additional step that would help to ensure that your new fish get the best possible conditions. This would only work if the water that you use to carry out the water change has a lower nitrate level than that which exists in your fish tank. It is worth checking this as levels in tap water, for instance, can legally be up to 50 mg/litre.
Step 7 – Add some hardy fish.
Once you are consistently recording zero levels of ammonia and nitrite the cycling should be complete and you are now ready to add fish. Nevertheless less, you should still proceed with caution. Do not jump from no fish to a fully stocked tank. Stock with small, hardy fish and allow for future growth. So if you have calculated that your aquarium can hold 10 mature fish only stock with 10 small fish. Do not feed at full rates initially. This is a very risky time however well you have matured your filtration system. Even with excellent water quality new fish need time to adapt to their new environment. Adding fish will invariably alter the water conditions further. Their environment will change and be different to that they have been used to.
Step 8 – Follow a strict quarantine procedure.
I cannot talk about introducing new fish into a fish pond without bringing up the subject of quarantine. Fishless cycling will go a long way to ensure that the filtration system is up to the job from day one. A certain amount of stress is inevitable however whenever a fish is introduced into a new environment. Many fish will have experienced several changes in their environment as they are passed from fish farm production ponds to holding tanks to airline transportation systems to wholesaler to retailer before they even arrive at your spanking new tank. It is almost inevitable that they will be carrying some fish parasites. Reputable fish dealers are worth their weight in gold when they carry out a proper quarantine procedure. Quite rightly biosecurity plans are now becoming the norm throughout the farming industry and are often a legal requirement. Ignoring this aspect of fish keeping has proven to be devastating to many sectors of our hobby . Fishless cycling can be a useful aid when establishing a new tank but proper quarantining will always be infinitely more important.