The Nitrogen Cycle

[delmore]

[quote author=Carol_Roberts link=board=2;threadid=934;start=15#msg169174 date=1076542411]
I think ammonia itself raises the pH.
[/quote]Right. From speaking to others that have fishless cycled, sometimes the pH rises, sometimes not. I assume it has to do with the particular minerals in the water that make it "hard" - calcium carbonate or whatever. If the pH rises too much, the cycling process slow, so it is not a bad idea to monitor it.

[aziyaeian]

I understand why should I test the amount of ammonia and nitrite. But I can't find that why should I test the nitrate. I used to change water regularly so am I ought to test nitrate?
Does testing nitrate or nitrite help me to find the amount of ammonia?

[ronrca]

Depends on what you term regular (daily, weekly?)! Stocking density, feeding (what type of food and how often) and % of wc will all affect the nitrate level. For discus, very low or no nitrates are best therefore testing on a regular bases should establish your wc schedule. Depending on the setup, some tanks only may only require 25% daily where as others may need 75% daily to maintain very low nitrate levels.


HTH

[A.J.]

At what level does the amount of nitrates become harmful to your fish? I just did a test on the water of my fish tank and the ph was at 6.4, ammonia was at 0, nitrite was at 0, and the nitrate level was at 5.0.

[Hans Kloss]

At what level does the amount of nitrates become harmful to your fish?

Depending on fish strain. The most nitrates sensitive fish I ever kept were dwarf suckers (otos) and elephant nose (Gnathonemus petersii). Prolonged nitrates concentration of 30 ppm is unacceptable for them and they die during several months. Discus are not very sensitive to nitrates but they need clean water, free of other pollutants.
Hans

[wbzorker]

Discus are not very sensitive to nitrates but they need clean water, free of other pollutants.
Hans

Hi Hans,
Would you mind clarifying "other pollutants"? I'm thinking that you might mean the heavy metals, phosphates and liquid bio waste. Am I right?

Thank you for your time,

[Hans Kloss]

Hi Hans,
I'm thinking that you might mean the heavy metals, phosphates and liquid bio waste.

I've never seen discus poisoned with heavy metals or phosphates. In fact this kind of poisoning is almost impossible until you use municipal water. But the real problem are "bio wastes". No, they are not very harmful, they only can feed bacteria. But big amount of bacteria in water is potentially dangerous for discus and can result with gills, skin, fins and eyes infections. Personally I treat nitrates only as an indicator of overall (including bacterial) water pollution.
Hans

[wbzorker]

Thanks, Hans.

[RockHound]

Nitrogen is found in aquaculture water in two basic forms, i.e., un-oxidized and oxidized nitrogen, as follows:

Un-oxidized forms of nitrogen include:
Ammonia (NH3)
Organic nitrogen (Org-N)
Nitrogen gas (N2)

Oxidized forms of nitrogen include:
Nitrite (NO2)
Nitrate (NO3)
Nitrous oxide (N2 O)

Nitrogen typically enters water as unoxidized nitrogen, in the form of organic nitrogen (Org-N) and ammonia. The combination of ammonia and Org-N concentrations is generally reported as total Kjeldahl nitrogen (TKN).

Although bacteria have various nutritional requirements, the main source of their food is in the form of organic and inorganic carbon.

In terms of carbon requirements, bacteria can be classified as:

Autotrophic bacteria (usually referred to as autotrophs) use inorganic carbon, such as carbon dioxide and bicarbonate, as their food source (for growth and reproduction), but also require other inorganic chemicals, such as ammonia, to supply energy. Autotrophs are instrumental to the ammonia removal process.

Heterotrophic bacteria (usually referred to as heterotrophs) use the organic carbon in wastewater as their food source (for growth and reproduction) and as a source of energy. Heterotrophs are instrumental in removing organic material from water and are instrumental in completing the nitrogen removal process.

An important distinction between heterotrophs and autotrophs is that autotrophic bacteria expend more energy for growth than heterotrophs, resulting in lower growth rates among the autotrophs.

Note: both are vital to the total nitrogen removal process.

Bacteria are also grouped according to their need for molecular oxygen (dissolved oxygen = DO) as follows:

Type of Bacteria Oxygen Requirements

Aerobic Can only exist when there is a sufficient supply of dissolved oxygen (DO).

Anaerobic Can only exist in an environment with minimal DO and derive oxygen chemically for respiration.

Facultative Can exist under aerobic or anaerobic conditions; prefer aerobic environments, so if DO is present in the water, they will consume it first, then derive oxygen chemically by utilizing nitrate, sulfate and carbonate (in that specific order).

With respect to the types of bacteria listed above, facultative heterotrophs play the dominant role in removing dissolved organic pollutants during a biological water treatment process.

The rate of growth of each type of bacteria depends largely on temperature, the type of food and nutrients available and the availability of DO. As you might guess, given an environment that has an ample food supply, but limited oxygen, it is the facultative bacteria that possess the greatest potential for survival and growth!

Role of Nitrifying Bacteria in Nitrogen Conversion:

Before examining the role of nitrifying bacteria in nitrogen conversion, it is important to understand that before nitrification can occur, most of the organic material present in the water must be removed. The removal of this organic matter is typically measured in terms of Biochemical Oxygen Demand (BOD) and is accomplished during secondary treatment by providing an aerobic environment for aerobic and facultative heterotrophs to consume the organic carbon.

This stage of BOD removal is often referred to as first-stage BOD removal or cBOD removal.

Once the cBOD concentration is sufficiently lowered, conditions become optimal for the growth of nitrifying bacteria (provided that sufficient levels of DO and alkalinity are available). The nitrifying bacteria use the DO and inorganic carbon to convert ammonia to nitrite and nitrate. The oxidation of ammonia to nitrite and nitrate is sometimes referred to as nBOD removal or second-stage BOD removal.

With that said, let’s now examine the ammonia conversion process.

In the process of nitrification, ammonia nitrogen is converted to nitrate utilizing purely aerobic autotrophs - the Nitrosospira & Nitrospira group of bacteria. All of which bacteria are instrumental in completing nitrification, the nitrification reaction in a two-step process as follows:

Step 1:
Nitrosospira bacteria, which are purely aerobic autotrophs, convert ammonia nitrogen to nitrite. During the conversion process these bacteria consume large quantities of DO and reduce alkalinity.

NH3 + Nitrosospira Bacteria + O2 + Alkalinity NO2 (Nitrite)

Step 2:
Nitrospira bacteria, which are also purely aerobic autotrophs, convert the nitrite (produced by the
Nitrosospira bacteria) to nitrate. Once again, the vital element needed for this conversion to occur is DO and the conversion process further reduces alkalinity. Nitrosospira have a faster growth rate than Nitrospira, therefore, once the ammonia is converted to nitrite, the conversion to nitrate occurs rapidly.

NO2 + Nitrobacter Bacteria + O2 + Alkalinity NO3 (Nitrate)

Role of Denitrifying Bacteria in Nitrogen Removal

Now that you have a basic understanding of how nitrifying bacteria converts ammonia to nitrate during biological treatment, let’s examine the role of denitrifiers in nitrogen removal.

In the process of denitrification, nitrate, the form of nitrogen that results from the completion of the nitrification process, is converted to nitrogen gas, utilizing facultative heterotrophic bacteria. The process of denitrification occurs under anoxic conditions as follows:

NO3 + Denitrifying Bacteria + Organic Carbon Nitrogen Gas + Water + Alkalinity

There are two steps required to achieve denitrification, i.e. nitrate removal.

Step 1- The nitrification process is reversed, and nitrate (NO3) is converted back to nitrite (NO2).

Step 2- Nitrite is converted to nitric oxide (NO), then nitrous oxide (N2O) and finally to nitrogen gas (N2).

The completion of the denitrification process can be summarized as follows:

NO3 > NO2 > NO > N2O > N2

There are two main requirements for successful denitrification.

1. Anoxic environment
Since facultative heterotrophs prefer to respire using DO, the denitrifiers will continue to respire
aerobically as long as DO is available. It is only when the DO is depleted that denitrifiers begin using nitrate for respiration, which begins the denitrification reaction.

2. Sufficient amount of organic carbon
Without organic carbon as the food supply, facultative heterotrophs cannot continue to grow,
multiply and thrive. Organic carbon can be supplied to the denitrification phase of biological treatment using influent water (which contains cBOD), and/or supplemented with either an ethanol, or a sugar solution.

One final point: Biological denitrification converts nitrate to nitrogen gas. Which is typically gassed off in an aerated chamber that follows the denitrification process.

[Hans Kloss]

Excellent summary, RockHound. Must-read for every fishkeeper.
Hans

[illusionkid6]

Just the article I needed to read. Working on setting up my first Discus tank and need all the help I can get.

[Apistomaster]

Plenty of good info in this thread but I want to address the myth that biological filtration does not work in extremely soft and acid water. For example a tank with 20 ppm TDS and a pH between 3.5 and 5.0.
There are species of bacteria that do fill this niche. I think the myth that bio-filtration doesn't work in the lower range came from experiences where hobbyists made change too quickly.

I have run tanks with a TDs of only 20 to 25 ppm TDS at a (pH between 3.5 and 4.0 for several years at a time.)
In this more extreme soft and acid water the bacteria which are adapted to the low end do the job but are not as efficient as those that prosper at more typical ranges.
Just kept it in mind and allow the Discus more space than the commonly recommended 10 gal per adult Discus. The system will work and Heckels and Greens will thrive.

There is no justification for keeping any Domestic Hybrids or wild S. haraldi in such extreme low hardness and pH parameters as they are naturally adapted to thrive in water which is considered by most to be "normal".

[Kevinh]

Really Good information. My tank is new (3.5 weeks) and this explains why my nitrites level is raising. So I'll start doing more water changes and monitor. Thanks

[cro117]

awsome post rockhound. i was going to add my simple explanation of denitrification, but you did it way better. i'm guessing you work in water treatment? i guess the only thing i have to add to this thread then is a bit more of an explanation of why nitrification lowers the ph, most of the time not even noticable.

heres a simplification of nitrification:

organic + 175 O2 → 122 CO2 + 16 NO3- + 16 H+ + 138 H2O ------- so basicly oxygen+waste > nitrate + carbon dioxide +water + H+ ion

the significance is that ph is simply just ions. water is H20 and if you split those you get H+ and OH-. H+ is acidic, OH- is alkaline. if you have very soft water and low carbonates and bicarbonates the ph swing will be a little more significant. so if you have well stocked tank turning over a significant amount of organics all the time, you will notice the ph getting lower every year.

[cro117]

oh, and as to rockhounds post, you can achieve a completed nitrogen cycle in your own tank extremely simple by adding a deep sand bed. just be careful as there are gases dangerous to your fish produced in the lower levels. if left undisturbed they are neutralized as they diffuse up to the surface and are oxygenated. so as long as you don't say pick up a deeply embedded rock disturbing the sand or something they are nothing to worry about. every tank i have i use a deep sand bed, and i have never had a sulphate die-off.

as far as a carbon source, detritus that makes its way below the sand will act as a descent source, but you can enhance the process by adding others.