Cycling a fresh water Aquarium.

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Cycling a fresh water Aquarium.

Postby Anthony on 05 Apr 2008 15:55

Cycling an Aquarium.
The most important part of keeping fish is understanding the
Nitrogen cycle. This is the process by which fish waste (Ammonia) is changed into a harmless/ less toxic substance (Nitrate) that won`t kill your fish.
Fish produce Ammonia (nh3)through fecal waste and through their gills.Rotting food and plant matter also produces Ammonia. This Ammonia is highly toxic to fish and will eventually kill them. What happens through the Nitrogen cycle is that Ammonia is broken down/processed by Bacteria(nitrosomanas) into another toxic substance called Nitrite(no2). This Nitrite is then broken down by another Bacteria(nitrospira) into Nitrate(no3) which in small doses is harmless to fish. A weekly or bi weekly water change then reduces the levels of nitrate in your tank keeping your fish healthy.


When starting off a tank you cannot add fish straight away. It must be cycled. Cycling a tank can be done in at least three different ways.
1) You can add Ammonia to your tank.

2) You can use hardy fish to produce Ammonia.

3) A kick start.

All three have their pros and cons.
1)Adding pure Ammonia can cause an adverse effect. Instead of Culturing(growing ) you can add too much and actually kill the Bacteria and in doing so slow the rate at which your tank is being cycled. Depending on the size of your tank adding a few drops of pure Ammonia daily should not be a problem. The levels of Nitrite will start to increase and the Ammonia levels will eventually drop to zero. As your levels of Ammonia begin to drop and you Nitrite starts to rise, another bacteria will begin to grow and start breaking down your nitrite. Nitrate levels wil begin to rise. Stop adding the Ammonia once you see Nitrate levels increasing in your tank. Eventually when you have zero Ammonia, zero Nitrite and readings of Nitrate your tank is cycled. A water change is needed to get the levers of nitrate to below 20 mg/l . Then you can add your first fish. It is very important to test your water daily with a reputable water test kit every week so as to not cause an Ammonia spike. The Bacteria in your tank needs to multiply to be able to break down the extra Ammonia produced by the increased fish load. Adding too many fish too fast will over load your filter and Ammonia levels will start to increase in your tank killing your fish.

2) Using fish to produce Ammonia is another way to cycle a tank. The same principles apply as adding pure Ammonia only small water changes are required to keep the levels of Ammonia very low so your fish don`t die during the process. Hardy fish like Goldfish are usually used as it can be
very stressful and even fatal on the fish. Anabantoids like Gouramis are probably better to use
because they use their Labrinth organ(a modified lung) as their primary breathing organ.

3) The best and quickest way in my opinion to cycle a tank is to get what is called a kick start from a mature filter. What you do is take a bio sponge from a mature tank and squeeze this straight in to a fish bag containing water from the chosen filters tank. This water can be throw straight into your new tank and fish can be added straight away. Or you can get some bio balls/tubes straight from the mature filter and add these to your new filter.

Things to remember.
1) Tap water contains Chlorine. Chlorine is a Bleach and Bleach kills fish as well as Bacteria. Always add De-chlorinator to you water before adding it to your tank.
Use a test kit to make sure your tank is cycling properly. New fish should be added no more than 2 every two

2)While doing water changes you will need to replace your white mechanical filter with a new one. This is used to take out any physical waste in your tank.

3)Always wash your Biological sponge/ balls/tubes in tank water. Never use tap water. The Chlorine in your tap water will kill the Bacteria in your filter causing an Ammonia spike in your tank killing your fish.

4)Test your water regulary. A clean tank is a healthy tank.
Last edited by Anthony on 05 Apr 2008 23:28, edited 1 time in total.
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