Well, I want to try it again. Byron said you need those anaerobic areas in a healthy system. That sounds right to me even though I don't understand why. I like an aquarium that looks as natural as my imagination envisions what I would see if I was actually right there underwater in South America or wherever. Seems to me also that plants would thrive in it. And I also agree that Corydoras and others need that. I have read substantiation of that. Something to do with their barbels. Thank you for the information. I have to give it a go and will let you know how it turned out. One other quick question. Depending on the type of rock the sand is crushed out of, does it tend to buffer the water to an alkaline pH ?
Play sand is inert, so it will not affect water chemistry. It is the most refined of the industrial sands so it is safe for fish that sift it through their gills (cories do this which is why they need sand), and safe for their softer underbelly.
You can acquire calcareous sands such as crushed coral/aragonite that are intended for marine tanks, and rift lake tanks; these dissolve calcium and magnesium to increase GH and KH and pH, necessary in such tanks. Also work for livebearers. But should never be used for soft water fish species.
On the anaerobic issue, the following excerpts from an article I authored elsewhere a few years ago may explain it.
The bacteria responsible for this 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.
Denitrifying Bacteria
These heterotrophic bacteria, of which there are several species, 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.
Waste Control Bacteria
These 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, 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.
Substrate 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 significantly, 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.
[6] Strohmeyer, Carl, “Nitrogen Cycle and Aquarium & Pond Cycling,” American Aquarium Products website.
