http://www.americanaquariumproducts.com/Nitrogen_Cycle.htmlThere's a lot of confusion among aquarists about nitrifying bacteria. This is due in large part to the recent emergence of a wide variety of bacterial products claiming to be nitrifying aids. Most of these products (all dry products in particular) actually contain species of Heterotrophic bacteria from the genera Bacillus, Pseudomonas, Escherichia, and others (as these bacteria are much easier packaged with a reasonable shelf life under normal conditions/room temperatures). Although a few better "sealed" (for shelf life) cycling products such as SeaChem Stability contain
facultative bacteria which can live in both oxygen and non-oxygen environments True nitrifying bacteria are
Autotrophic and considered to be those belonging to the family Nitrobacteraceae whose energy sources are derived from the chemical conversion of ammonia to nitrite, or, nitrite to nitrate (Autotrophic bacteria are organisms that produce complex organic compounds from simple inorganic molecules). They require oxygen, utilize mostly inorganic (without carbon) compounds as their energy source, and require carbon dioxide (CO2) for their source of carbon. In the case of the Nitrobacteraceae these energy sources are derived from the chemical conversion of ammonia to nitrite, or, nitrite to nitratThe desired Autotrophic aerobic bacteria of nitrifying bacteria are present everywhere (e.g., in the air), oxygen and at least some moisture is present (not in areas void of oxygen) [reference: 3].
It is important to note that although the desired nitrifying species of bacteria are “all around us”, they do not readily store in sealed oxygen free containers (
dying rapidly or going dormant without oxygen to the point of long periods to revive); it takes some time for the sparse air born nitrifying bacteria to populate an aquarium or pond, so do not expect these bacteria to “magically” populate your aquarium overnight, even a re-started aquarium will need to be re-populated (please see cycling methods further down in the article).e.
Heterotrophic Bacteria are an organism that requires organic substrates to get its carbon for growth and development.
Some are strictly aerobic, but many are facultative anaerobes (they can survive in either the presence or absence of oxygen). Heterotrophic Bacteria are generally found in most over the counter aquarium cycling products (especially "Sludge Removers") due to their portability.
Heterotrophs can be either gram-positive (ex: Bacillus) or gram-negative (ex: Pseudomonas) which in the case of Pseudomonas many gram negative aquarium treatments (such as Kanamycin) can be effective against Pseudomonas while not harming true Autotrophic nitrifying bacteria.
Another point is growth (which is why Heterotrophic bacteria are favored for cycling products); nitrifying (Autotrophic) bacteria will double in population every 15-24 hours under optimal growth conditions. Heterotrophic bacteria, on the other hand, can reproduce in as little as 15 minutes to 1 hour.
Unfortunately research has shown that up to one million times more of these heterotrophic bacteria are required to perform a comparable level of ammonia conversion that is attained by true autotrophic nitrifying bacteria, in part due to the fact of Heterotrophic Bacteria to convert many organics into food.The use of only Heterotrophic Bacteria to cycle an aquarium (or pond) can result in a bio environment that does not contain the necessary Autotrophic nitrifying bacteria to rapidly adapt to changes in bio load either from added fish, wastes, or similar; thus often resulting in sudden spikes in ammonia or nitrites when these Heterotrophic bacteria cycling products are not added in a timely or regular schedule!
The other danger is cloudy water
Denitrification
is the process by which microorganisms convert nitrate (NO3) to nitrogen gas (N2)
This process is more common in Marine aquaria and takes place in fine #00 sand, live rock, or “aquarium mud”.
In freshwater aquariums this process often produces potentially dangerous Hydrogen Sulfide, but by maintaining an oxygen level above 1 ppm, this can be avoided. Plants roots are great for maintaining this balance of oxygen in the gravel for proper Nitrate removal by allowing very small amounts of oxygen into the substrate which promotes nitrogen reduction over sulfur reduction (which occurs in substrate with 0 oxygen).
As a generalization, aerobic nitrification takes place in the top 1-2 inches of substrate (deeper in courser substrate, or more shallow in fine sand). While nitrogen fixing anaerobic bacteria oxidize nitrates in an area of 2-4 inches of substrate (again deeper for course media, more shallow for fine sand). Finally Sulfur fixing anaerobic bacteria that produce hydrogen sulfides generally live in substrate over 3-4 inches in depth.
A tell-tale sign of Hydro Sulfide production is black areas in the deep areas of sand or substrate, whether freshwater, marine, or especially ponds. The rotten egg odor is another sign although as Hydrogen Sulfide levels in the air increase, research has shown that humans olfactory senses tend to block out the smell.
One key to allow de-nitrification without production of Hydrogen Sulfide is to allow some oxygen penetration of the substrate and as well. In saltwater aquariums, worms, copepods, etc often help perform this work. In freshwater, plant roots achieve this well and also remove raw ammonia as well as nitrates.
neljutim se i mogu kao sto vidis

neke prezive neke ne, za druge kazu da su korisnije. a ove sto prezive..u uvjetima bez kisika u filteru se stvara
http://en.wikipedia.org/wiki/Hydrogen_sulfideneznam koliko bakterija moze pobiti ali pustiti to natrag u akvarij kod riba...