Ways how to Cycle an Aquarium

Aquarium cycling with fish

This method is used for keepers who are adding fish to their aquariums straight away, the fish used must be very hardy as sensitive fish will suffer during this cycling method. If possible try to get hold of some filter media from an established aquarium and add it to your filter, this will kick off the cycling process straight away. If you cannot get any media it will mean that the aquarium cycling process will take longer, anything up to 6 weeks. Once the hardy fish are added to the tank you will start to get ammonia readings with your test kit. These readings will continue to rise as the bacteria in the filter are still colonising and until the colony is large enough they will not be able to cope. Once the ammonia has peaked the ammonia results will start to drop and the readings of nitrites in the water will start to rise. This will mean that the bacteria which convert the ammonia into nitrites have now colonised to a large enough colony to deal with the first part of the aquarium cycling.

Eventually the readings for nitrites will peak and drop to 0, this means that the beneficial bacteria are now converting the nitrites into nitrates, these are less toxic than ammonia and nitrites so now you are well on the way to your aquarium cycle being completed. The only way to remove nitrates is to perform regular water changes so now is the time to start this, readings of below 40 for nitrates means that the aquarium is cycled and you will now need to keep performing your water changes to keep the nitrates at a constant level.

Key points to remember with this method of cycling are:-

• Test your water daily, you need to know exactly how the cycle is doing.
• Always check your fish for any signs of stress, as mentioned above, only hardy fish should be used with this method of aquarium cycling.
• When you add more fish to the aquarium, keep testing the water and don’t add any more fish until the readings are back to normal.
• You may experience algal blooms during the cycling process especially when cycling with fish in the tank, this is normal and the blooms should disappear once the cycling is complete.

Aquarium cycling-the fishless method

This is the preferred method on most fish keepers nowadays, the aquarium can be cycled without placing any possible stress on fish and will often provide stronger bacterial colonies in the aquarium filters. It can be achieved by three different methods but the results will always be the same. Commercial bacteria cultures can be used, these are simply added to the aquarium following the instructions on the bottle, these work for some keepers bot some are biased against them. The second method is to add some fish food to the aquarium and allow it to decay thus producing ammonia, this method does work but controlling the ammonia levels in the aquarium is a bit hit and miss. I much prefer using pure ammonia, you know exactly how much is being added to the aquarium and you can control the levels to suit the stage of the aquarium cycle. This is the method I will explain below:-

The ammonia used must be pure, there are perfumed ammonia bottles for sale, these will not be suitable for the aquarium as they will add harmful toxins to the water that will remain after the cycle has been completed. Using the pure ammonia add a few drops at a time, with the first dose you will have to repeatedly test the water with a suitable testing kit until you reach an ammonia level of 4-6 ppm. Do not test the water as soon as you have added the ammonia, stir the water and test after an hour. Count how many drops it took to reach the required level, this will help you work out how much ammonia is needed with each dosing. Repeat this process every day until the ammonia readings start dropping when you are still adding the same dosage, this means that the ammonia has peaked and bacteria are now converting this to nitrites. Now is the time to start testing for these with your testing kit.

After a few days of repeatedly dosing your tank the nitrites should also start to drop, nitrates are now in the aquarium water, test for nitrates to check on this. Once nitrates are in the water your aquarium cycle is nearly complete. The nitrites will drop to zero and the nitrates can be removed by regular water changes. Now your filters are ready for fish to be added to the tank!

There are a couple of points to remember using either method of cycling your aquarium:-

• Cycling your tank can take up to 6 weeks, do not try to rush this process, let it run its own course and your fish should have no problems when placed into the tank.
• During the cycling process do not perform any water changes until the nitrites show a reading of zero, doing water changes during the cycling process will mean that the cycle will take longer to complete.
• Keep a log of your test results, this way it will become more obvious when the ammonia or nitrites have peaked, this is a lot easier than trying to remember the test reading results in your head.

Questions and answers

On March 18th 2011 we merged all related questions and answers from aqua-fish.net/answers with this article in order to put all related information together. Some of the answers listed below may have been answered partially in the article above, however it's easier to find a particular answer within a list instead of sentences in text. All questions were asked by visitors of Aqua-Fish.Net and you're welcome to ask too! Simply fill the form at the bottom of this page and ensure that you're asking something that isn't answered here yet.

• Why are nitrate levels important?Answer: Monitoring nitrate levels in the aquarium is important; if they are allowed to reach a high level for a length of time the fish‘s health will start to suffer, they are not as toxic as ammonia or nitrites but still not good for the fish or plants.
• What causes high concentration of nitrite and nitrates?Answer: Too much of fish excrements in general. If excrements aren't decomposed by nitrification bacteria present in the tank, they cause problems. More in this article: link.
• Which bacteria break down nitrite in the aquarium?Answer: Nitrospira is the bacterium that breaks down nitrite in the aquarium, turning into nitrate which is a less harmful chemical for fish. It is a slow growing organism that can take between 12 and 32 hours to multiply.
• Which tropical aquarium fish are immune to ammonia and nitrite?Answer: There are no fish that are immune to ammonia or nitrite. There may be some fish that are more tolerant to the presence of these two chemicals but inevitably the same effects will take place on every fish in the presence of ammonia and nitrite.
• What causes nitrite levels to rise in aquariums?Answer: This is caused when your aquarium has had an ammonia spike and the bacteria in aquarium begins to use the ammonia as an energy source which produces nitrites as waste.
• What nitrite level is toxic to fish?Answer: Any nitrites in your tank are extremely toxic to your fish. If the tank has been cycled properly there should be no nitrites present as the bacteria in your filter will have converted them all to nitrates.
• What are Nitrite, Nitrate and Ammonia?Answer: Ammonia is NH₃; is a chemical that is highly toxic to fish even in small amounts.Nitrite is NH₄ ; is also toxic and can be harmful towards fish.Nitrate is NO₂^-; is seemingly harmless towards fish but in higher concentrations it is not.
• Why is ammonia more toxic than nitrates?Answer: Ammonia in aquarium water will cause gill burning and respiratory problems with the fish, nitrates have a less damaging impact of the fish’s physical well being.
• Why do we get high nitrates when cycling the aquarium?Answer: This is because the filter is now converting all of the nitrites into nitrates. At first this will be high but water changes will drop the nitrate level.
• What causes nitrate levels to rise in aquariums?Answer: Nitrate levels rise when bacteria in your aquarium break down existing nitrites for energy, this produces nitrates as waste. Nitrates should to be removed by water changes.
• What should the nitrate levels be in the aquarium?Answer: In an ideal world, the nitrates would be at zero; however this is rarely the case and most nitrates will run at 5-10. The fish will be OK with this level but if they start to rise, then larger water changes are required.
• What should I do if my freshwater tank has nitrite and nitrate spike?Answer: The two will never spike together, as the nitrites spike the nitrates will grow as the bacteria convert them to nitrates but once this occurs the nitrites will drop rapidly. The only way to remove high nitrates is to do large water changes until they drop.
• What time of day are nitrates highest in aquarium?Answer: Nitrates gradually build up between water changes; there is no particular time of day for a nitrate peak.
• What are nitrates or nitrites and how harmful are they?Answer: Nitrites are produced when ammonia is broken down by the beneficial bacteria in your aquarium. Nitrites are then used as a energy source for the bacteria and nitrates are produced. However, as levels of nitrates increase; the harmful effects they take on your fish increase as well. Levels of nitrate can be reduced by doing water changes.