Handout: Cycling a Fish Tank

Optional Reading and Additional Information:

Cycling a Fish Tank:

Nitrogen Cycle

​We are waiting to put fish into this aquarium. 
Why?
 
When an aquarium is first set up, especially one using real soils and fertilizers to grow living plants, the ammonia levels are dangerously high for fish.  In a mature system bacteria convert ammonia from fish waste and soils to Nitrites, then to Nitrates.  At each step in this ammonia cycle (actually called the nitrogen cycle) the product is less toxic.  So high concentrations of ammonia are the most dangerous to fish, while nitrates are relatively harmless.  We want these these nitrates in the system because they are important as plant fertilizers. 

Helpful bacteria must be given time to grow in an aquarium.  These bacteria are essential for changing ammonia to nitrites and nitrites to nitrates to make the water safe for fish and plants to live together.  We are waiting for these healthy bacteria to grow in this tank before adding fish.  This process is called Cycling an Aquarium because it gives time for this nitrogen cycle to start.
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Growing plants in a fish tank requires the right balance of many things including ammonia, nitrites, nitrates, oxygen and carbon dioxide. We are regularly testing for these indicators to know when to add additional residents.  It can take weeks.

Here is this handout in printable form:

cycling_an_aquarium.pdf
File Size:	384 kb
File Type:	pdf

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Day #1: 11-5-2017 Update

On Sunday we assembled many of the systems (Ex: filter, pumps, heater) and the hardscape (rocks and dirt) for this aquarium.  The soil in the aquarium is high in Ammonia for fertilizer which will eventually make the ammonia levels in the water spike to above 2.0 ppm before healthy bacteria grow which convert that ammonia to nitrites and eventually to less harmful nitrates which plants can use.  An ammonia level above around .5 ppm would be considered lethal to most inhabitants.  Want to know more:  https://www.algone.com/ammonia-in-the-aquarium-and-its-effects-on-fish-life

When Measured on this first day ammonia was still leeching from the soil and the levels in the aquarium haven't climbed very high yet. 

The test results provided by students were as follows:

pH: 6.0
Ammonia: 0.3ppm

Nitrites: 0.0ppm
Nitrates: 0.0ppm

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Day #5: 11-10-2017 Update

The water clarity and turbidity is improving considerably, however it is the invisible ammonia levels that we are most concerned with.  See the results below.

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pH: 6.0
​Ammonia: 2.0ppm

Nitrites: 0ppm
​Nitrates: 0ppm

As expected the ammonia levels from the soil fertilizer are at toxic levels for fish.  It will be a while longer before fish can be added as these need to drop almost to 0ppm before fish can be added.  In the nitrogen cycle these ammonia levels will drop as nitrite levels rise.  Then nitrite levels will drop as nitrate levels rise.  Once our nitrate levels are higher and the ammonia is low we can add fish.  We can see by the low nitrite and nitrate levels that the cycle is just getting started. 

​The pH level is low, this is also expected because organic materials in the soil will usually lower pH.  Before we add fish we may need to adjust the pH up to 6.5, but we can make that call later.