There have been a lot of threads about nitrification and cycling lately. IMO - the most important measurements tool you have in order to indicate if your cycle is done or not is the nitrite level. It is a rather stable tool and will give stable results with few interferences. One of the myths about nitrite (NO2) is that it should be 0 in a working aquarium. This is not really the truth - it has been shown that concentrations between 0.01 and 0.05 is rather common in reef aquariums. In freshwater aquariums - nitrite is one of the most important tests in use. This is because nitrite in freshwater is rather deadly. Fish take up nitrite from the water through the gills. When nitrite reaches the blood in the fish - it reacts with haemoglobin (the compound responsible for oxygen uptake and transport in the blood) and form methaemoglobin - a substance that is brown and does not bind or transport oxygen. Further on - it has been shown that chlorides in the water will block this uptake of nitrite from the water, hence nitrite is non-toxic for saltwater fish - it will not come into the bloodstream at all.
The acceptance that nitrite is non-toxic in saltwater has led to measurements of nitrite in saltwater to not be as common any longer. However - for me it is one of the more important measurements of different reasons.
Nitrite is formed inside the aquaria from the microbiological processes that always take place and mostly through two major pathways.
Pathway 1
A bad working nitrification process.
The nitrification process consists of two different parts.
The first step is the ammonium oxidation step. This step can be done of many different bacteria strains (AOB) and by different types of archaea (AOA). It starts rather quick and can happen in oxygen levels down to 3 – 4 ppm. It is an important step because it is especially important that total ammonia should not build up into concentrations that allow high levels of the toxic form – ammoniac (ammonia gas or NH3) – in the water. How much of the total ammonia that consist of the toxic form (NH3) is mostly depended on pH, salinity and temperature. This tool can be a help
The second step is nitrite oxidation into nitrate. This step is done by few bacteria (NOB) – mostly from the genus Nitrobacter and/or from the genus Nitrospira (or Nitrospira like)
This step is more sensitive and often needs oxygen around 5 ppm. It seems also that they need more phosphate in the water in order to have a good growth – and there are some reports that indicate that high ammonia concentration stops this step. The result of a stoppage is that high levels of nitrite will be built up. A nitrite check during the start of the cycle is a good tool that indicate that the cycle is done the whole way. When nitrite levels are down below 0.05 – it is ok – IMO.
Pathway 2a
Pathway 2a is the normal denitrification process. Sooner or later - the denitrification process will start in nearly all aquarium - especially in those with sand beds. This process - in order to be fully completed - demands nitrate, an anaerobic environment and some type of DOC source (external or internal). If this process is not fully worked out – there can be a nitrite build-up.
Pathway 2b
If you use a sulphur-based denitrification – a not fully completed process can result in nitrite build up in the water column if there is not enough filtering capacity for the nitrification pathway.
If nitrite is not toxic in saltwater – why worry?
As I know it – most investigations have been on gill breathing animals with haemoglobin as an oxygen transporter in the bloodstream. There are few other – if any -investigation according animals not using haemoglobin as oxygen carrier and/or in animals that have different oxygen uptake mechanisms than gills. You can´t be sure that there are not animals that take up nitrite in the bloodstream and get into a situation with low uptake of oxygen.
Further on – bacteria and archaea that are important for the nitrification process are oxygen using autotrophs and slow growers. They compete with fast-growing heterotrophs for both oxygen and space to sit on. There is indications that the second step is more sensitive for competition and a build-up of nitrite in a mature system. This can be caused by too much organic load in the system. This is also the reason why we should not add either DOC (dissolved organic carbon) or heterotrophic bacteria in the start of an aquarium. Only nitrifiers should be added in the start. Nitrite measurements in the start cycle show us when the cycle is done, and we can go further with the creation of our unique ecosystem. IMO – this is also the reason why the “rotten shrimp method” should be avoided in the start. If you start with chemical addition of NH3/NH4 and bottled nitrification bacteria it is essential to know when the nitrite spike is gone IMO. If you start the aquarium the way I have outlined in my 15 steps – you will not have a nitrite spike at all IME.
In a mature aquarium – denitrification will happen. In anaerobic (without oxygen) environment many heterotrophic bacteria can shift from oxygen to nitrate as a metabolic electron acceptor and nitrogen gas will be the waste from that process. This process is named denitrification. However – in this process they need an electron donator too – the denitrification bacteria can use different types of DOC as donators (Dissolved Organic Carbon). If the DOC level is too low – the denitrification process will leak some nitrite and if there is to less nitrification filtering capacity (and – IMO – it is often the case in reef aquarium – some do not want “nitrification factories” – one of the myths – IMO). Nitrite will build up in the water column – a measurement of nitrite will tell us if something happens. It is important to stress that too low DOC concentrations led to nitrite build up by halting the denitrification process and too much DOC led to the inhibition of the nitrification process and further build-up of nitrite in the aquarium. A proper translation of the Swedish word “lagom” would be a good tool here – Lagom means not too much and not too little – maybe – just enough or just right is the proper English expression here.
Nitrite measurements as a tool for proper care of the ecosystem – yes – but can it have other advantages as well?
Many of us measure nitrate as one of the key parameters in our reef. There is a discussion about levels of nitrate. Many uses 5 – 10 as a guideline, other want it to be between 0.5 and 5.
All hobby tests I know (with exception of the upcoming ION director from GHL) are based on the same principle. A metal salt is in use to reduce the nitrate into nitrite. The test reads nitrite but after a certain time when x % of the nitrate has been converted into nitrite. The colour chart translates back the nitrite reading into mg/L nitrate with a certain conversion factor. This factor is depended on brand and metal salt in use but vary from 50 to 100 times. It means that if there is nitrite in the sample from the beginning – you will have a too high reading. The brand I use for the moment (Tropic Marine PRO nitrite/nitrate test. Fauna Marines PRO seems to be the same type) have 100 as a multiplying factor. It means that if I have 0.02 mg/L of nitrite from the beginning – my nitrate readings are 2 mg/L too high. 0.05 ppm nitrite from the beginning -> 5 ppm too high nitrate reading. As I have seen – it is rather normal with these nitrite readings in mature reefs and if I want to have Nitrate levels below 5 mg/L I must analyse my nitrite concentrations in order to get a decent (and right nitrate reading)
IMO even nitrate readings up to 10 mg/L can be very wrong if you do not know your nitrite readings.
As I see it – there are a lot of reasons why nitrite readings should be done both in newly started aquariums and older more mature tanks.
Sincerely Lasse
The acceptance that nitrite is non-toxic in saltwater has led to measurements of nitrite in saltwater to not be as common any longer. However - for me it is one of the more important measurements of different reasons.
Nitrite is formed inside the aquaria from the microbiological processes that always take place and mostly through two major pathways.
Pathway 1
A bad working nitrification process.
The nitrification process consists of two different parts.
The first step is the ammonium oxidation step. This step can be done of many different bacteria strains (AOB) and by different types of archaea (AOA). It starts rather quick and can happen in oxygen levels down to 3 – 4 ppm. It is an important step because it is especially important that total ammonia should not build up into concentrations that allow high levels of the toxic form – ammoniac (ammonia gas or NH3) – in the water. How much of the total ammonia that consist of the toxic form (NH3) is mostly depended on pH, salinity and temperature. This tool can be a help
The second step is nitrite oxidation into nitrate. This step is done by few bacteria (NOB) – mostly from the genus Nitrobacter and/or from the genus Nitrospira (or Nitrospira like)
This step is more sensitive and often needs oxygen around 5 ppm. It seems also that they need more phosphate in the water in order to have a good growth – and there are some reports that indicate that high ammonia concentration stops this step. The result of a stoppage is that high levels of nitrite will be built up. A nitrite check during the start of the cycle is a good tool that indicate that the cycle is done the whole way. When nitrite levels are down below 0.05 – it is ok – IMO.
Pathway 2a
Pathway 2a is the normal denitrification process. Sooner or later - the denitrification process will start in nearly all aquarium - especially in those with sand beds. This process - in order to be fully completed - demands nitrate, an anaerobic environment and some type of DOC source (external or internal). If this process is not fully worked out – there can be a nitrite build-up.
Pathway 2b
If you use a sulphur-based denitrification – a not fully completed process can result in nitrite build up in the water column if there is not enough filtering capacity for the nitrification pathway.
If nitrite is not toxic in saltwater – why worry?
As I know it – most investigations have been on gill breathing animals with haemoglobin as an oxygen transporter in the bloodstream. There are few other – if any -investigation according animals not using haemoglobin as oxygen carrier and/or in animals that have different oxygen uptake mechanisms than gills. You can´t be sure that there are not animals that take up nitrite in the bloodstream and get into a situation with low uptake of oxygen.
Further on – bacteria and archaea that are important for the nitrification process are oxygen using autotrophs and slow growers. They compete with fast-growing heterotrophs for both oxygen and space to sit on. There is indications that the second step is more sensitive for competition and a build-up of nitrite in a mature system. This can be caused by too much organic load in the system. This is also the reason why we should not add either DOC (dissolved organic carbon) or heterotrophic bacteria in the start of an aquarium. Only nitrifiers should be added in the start. Nitrite measurements in the start cycle show us when the cycle is done, and we can go further with the creation of our unique ecosystem. IMO – this is also the reason why the “rotten shrimp method” should be avoided in the start. If you start with chemical addition of NH3/NH4 and bottled nitrification bacteria it is essential to know when the nitrite spike is gone IMO. If you start the aquarium the way I have outlined in my 15 steps – you will not have a nitrite spike at all IME.
In a mature aquarium – denitrification will happen. In anaerobic (without oxygen) environment many heterotrophic bacteria can shift from oxygen to nitrate as a metabolic electron acceptor and nitrogen gas will be the waste from that process. This process is named denitrification. However – in this process they need an electron donator too – the denitrification bacteria can use different types of DOC as donators (Dissolved Organic Carbon). If the DOC level is too low – the denitrification process will leak some nitrite and if there is to less nitrification filtering capacity (and – IMO – it is often the case in reef aquarium – some do not want “nitrification factories” – one of the myths – IMO). Nitrite will build up in the water column – a measurement of nitrite will tell us if something happens. It is important to stress that too low DOC concentrations led to nitrite build up by halting the denitrification process and too much DOC led to the inhibition of the nitrification process and further build-up of nitrite in the aquarium. A proper translation of the Swedish word “lagom” would be a good tool here – Lagom means not too much and not too little – maybe – just enough or just right is the proper English expression here.
Nitrite measurements as a tool for proper care of the ecosystem – yes – but can it have other advantages as well?
Many of us measure nitrate as one of the key parameters in our reef. There is a discussion about levels of nitrate. Many uses 5 – 10 as a guideline, other want it to be between 0.5 and 5.
All hobby tests I know (with exception of the upcoming ION director from GHL) are based on the same principle. A metal salt is in use to reduce the nitrate into nitrite. The test reads nitrite but after a certain time when x % of the nitrate has been converted into nitrite. The colour chart translates back the nitrite reading into mg/L nitrate with a certain conversion factor. This factor is depended on brand and metal salt in use but vary from 50 to 100 times. It means that if there is nitrite in the sample from the beginning – you will have a too high reading. The brand I use for the moment (Tropic Marine PRO nitrite/nitrate test. Fauna Marines PRO seems to be the same type) have 100 as a multiplying factor. It means that if I have 0.02 mg/L of nitrite from the beginning – my nitrate readings are 2 mg/L too high. 0.05 ppm nitrite from the beginning -> 5 ppm too high nitrate reading. As I have seen – it is rather normal with these nitrite readings in mature reefs and if I want to have Nitrate levels below 5 mg/L I must analyse my nitrite concentrations in order to get a decent (and right nitrate reading)
IMO even nitrate readings up to 10 mg/L can be very wrong if you do not know your nitrite readings.
As I see it – there are a lot of reasons why nitrite readings should be done both in newly started aquariums and older more mature tanks.
Sincerely Lasse
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I have not tested their saltwater test - but the freshwater works well. A rise in nitrite levels can give a signal that the NH
