To your question on the gravel depth, yes. Of course, "dead spots" can occur in any depth if oxygen/water flow is basically stopped by something.
On the second question, as I understand it from my research, the substrate is usually going to be "cleaner" than the dirty neglected filter, always assuming a biological balance exists in the aquarium. The biological processes occurring in the substrate are multi, unlike in the confined filter. And remember, we are talking a planted tank here.
Byron.
--- In AquaticLife@yahoogroups.com, "nonstopmom888" <ehebens@...> wrote:
>
> Hi Byron,
>
> thank you so much for the detailed info about the bacterial processes!
> It was great to read a compressed version with so much info in it!
>
> Just to make sure I understood it right:
> Coarse gravel layers thinner than 4 inches most likely promote the existence of beneficial bacteria (different types) and avoid the production of harmful hydrogen sulfide because they still enable enough oxygen throughput?
> There was only one point that was not clear too me: it was mentioned that the anaerobic bacteria multiply much faster than the nitrifying bacteria and might take over certain areas (like the filter) if not maintained properly... It seemed if the filter is not cleaned they might overwhelm the nitrifying bacteria while on the other hand in the gravel this does not happen? How is the balance maintained in the gravel and not in the filter? Maybe it is obvious and I just do not see it but I must admit I do not fully understand the interaction between the two bacteria types. Even through I am relieved that it seems the gravel balances it out somehow... :)
>
> Thanks again,
> Nora
>
>
>
>
>
> --- In AquaticLife@yahoogroups.com, "amphibian_ca" <bhosking@> wrote:
> >
> > I carried out a fair degree of research into the question of cleaning or not cleaning the substrate in planted tanks, and I will try to respond to the questions I noted in the threads on this topic.
> >
> > The bacteria responsible for the nitrification process of converting ammonia to nitrite to nitrate are termed nitrifying. But the nitrogen cycle is only complete (in aquaria) when it includes de-nitrification; in this stage, different bacteria that are termed denitrifying convert nitrate into nitrogen gas which is released back into the atmosphere. Another component of the complete nitrogen cycle in nature but not present in our aquaria involves the "fixing" of atmospheric nitrogen by cyanobacteria and other life forms.
> >
> > The denitrifying bacteria are heterotrophic bacteria, of which there are several species; they utilize nitrate by consuming the oxygen within nitrate and releasing nitrogen gas. They do not require free oxygen in the water so they are facultative anaerobes, and generally occur in what we term "dead spots," which occur when water movement is stopped and thus no oxygen is available. These are the good guys among heterotrophs, since de-nitrification is important in a healthy aquarium. And they will naturally occur in the lower level of the substrate as will be explained below.
> >
> > Some species of heterotrophic bacteria break down dead organic matter like fish waste, dead fish or plant matter, uneaten fish food, dead bacteria, etc. Some are aerobic, but many species are facultative anaerobes, able to live with or without oxygen. Like all bacteria, they colonize surfaces [in biofilms], and these are most prevalent in the substrate and the filter media. Many species can survive complete drying, allowing them to remain potent even when filter media that has been previously used is completely dry.
> >
> > These bacteria have only one requirement to appear and live: organics. They compete with autotrophic bacteria for both oxygen and surface area; studies show that even in relatively clean environments, they occupy more than 50% of the available surface area. And given that they can reproduce within 15-60 minutes—compare this to the 12-32 hours required by nitrifying bacteria—you can see how easily these heterotrophic bacteria can overwhelm the system. In a filter, if sludge is allowed to increase, heterotrophic bacteria will multiply so fast they actually smother and kill the autotrophic nitrifying bacteria.
> >
> > The greatest population of bacteria in a healthy balanced aquarium occurs in the substrate, not the filter. The floc or humic compost that collects in the substrate is the host for the biofilms; this is why the substrate in planted tanks should never be disturbed, and many aquarists apply this to non-planted tanks as well.
> >
> > In very general terms, aerobic nitrification takes place in the top 1-2 inches of the substrate; anaerobic de-nitrification takes place approximately 2-4 inches down, and anaerobic bacteria producing hydrogen sulfide occurs in substrates deeper than 3-4 inches. In all three cases, it will be deeper in coarse substrates (like pea gravel) and more shallow in finer substrates such as sand. These generalities will also vary with the presence of live plant roots and substrate "diggers" such as snails and worms, since these factors result in more oxygen being made available in the substrate, reducing anaerobic bacteria activity. An oxygen level in the substrate of as little as 1 ppm promotes nitrogen reduction rather than sulfur reduction (hydrogen sulfide). [6]
> >
> > Maintaining a substrate of fine gravel or sand no deeper than 4 inches, having live plants rooted in the substrate, and keeping Malaysian Livebearing snails are the best and safest methods of providing a healthy biological system for aerobic and denitrifying anaerobic bacteria.
> >
> > The above is excerpted from an article I compiled on bacteria in freshwater aquaria, and the source references are included. Those who want to see the sources will find the article here:
> > http://www.tropicalfishkeeping.com/freshwater-articles/bacteria-freshwater-aquarium-74891/
> >
> > Byron.
> >
>
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