How Does My Biological Filter Work?Published: Tue, 11 Aug 2009
The Nitrogen Cycle
The Nitrogen Cycle consists of 3 chemical compounds: Ammonia (NH4), Nitrite (NO2) and Nitrate (NO3).
Ammonia is created mainly from fish excretion and respiration but also from the break-down of proteins such as rotting food, plants or if a fish dies within a pond or aquarium and is not removed immediately. Around the East Yorkshire region we have very hard water as well as a high pH value (typically 8.0 – 8.2 out the tap) which makes the already dangerous ammonia even more toxic. Below is a table to show roughly what concentration ammonia becomes toxic (NOTE: Resistance to ammonia varies from fish to fish).
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Water temperature
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pH
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15oC (59oF)
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20oC (68oF)
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25oC (77oF)
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6.5
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19.7 ppm
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15.4 ppm
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11.1 ppm
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7.0
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6.4 ppm
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5.0 ppm
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3.6 ppm
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7.5
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2.0 ppm
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1.6 ppm
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1.2 ppm
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8.0
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0.6 ppm
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0.5 ppm
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0.4 ppm
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8.5
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0.3 ppm
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0.2 ppm
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0.1 ppm
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Ammonia levels in a newly established tank or pond will rise up to a level around 4.0ppm (parts per million). You may hear the Ings Lane staff talking about “good bacteria”. Around 7-10 days after the addition of the first fish, the ammonia levels begin to drop. This is due to one of these “good bacteria” known as Nitrosomonas oxidising Ammonia into Nitrite. Simply imagine that in one end of Nitrosomonas goes Ammonia and out of the other end comes Nitrite (it is a complex chemical process but this is the easiest way to picture it).
So now the Ammonia levels are decreasing thanks to Nitrosomonas bacteria, but it is being converted into another harmful compound known as Nitrite which is just as deadly to fish. Nitrite will slowly creep up to a level of roughly 4.0ppm about 3 weeks after the first few fish are introduced. Usually around 48 hours after Nitrite has peaked, the dangerous levels plummet to zero thanks to another type of bacteria know as Nitrobacter which converts Nitrite to Nitrate (again, use the same analogy from before if it helps). Both of these bacteria are available bottled in the form of API Stress Zyme and Tetra Safe Start and are ideal to be used to help the filter mature in its first few weeks or to top up existing bacteria levels when adding new stock to the aquarium.
Nitrate is a lot safer that Ammonia and Nitrite. Infact, Yorkshire Water will allow Nitrate out of our taps at 50ppm and anything under that level is just fine. However, high levels of Nitrate can cause stress and lead to problems such as velvet and whitespot. Nitrate is removed from our aquariums and ponds by plants taking the compound up as food, through water changes and also from being broken down into a harmless nitrogen gas and escaping into the atmosphere.
Article by Jackson Sage.
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