In response to Actinic's post in the goldfish thread, in which he refuted my claim of a tank not being a self sustaining system, i thought i'd start up a new thread, a-because a little bit of discussion would be good for any other fishkeepers to read and b-i get to talk fish so rarely these days.
My comment of 'tanks are a self-sustaining system, but some are more self-sustaining than others' (may not be exact wording) was in reference mostly to the action of denitrifying bacteria on fish waste products and the likes, since this is what i believed the wal-mart employee's comment to most be on about.
Your 'average' fish tank is semi-sustainable on a micro scale. Often chemicals can be recycled or decomposed by bacterial or faunal elements. On a macro scale, most tanks do not have the necessary food sources to permit any sort of major fish stocking levels.
There are partial exceptions to this. For instance, i'm currently running a small nano tank in the Amano style. It has 1 fan shrimp and three otto's, all of which seem to be doing hunky dory. The plants grow at such a rate i use the tank as a nursery, taking cuttings and growing them up in there before replanting back in the original tanks.
However, the tank still requires regular waterchanges. In a natural enviroment all those animals come from areas with flowing water, providing a constant turnover. In a small (20L) tank one must change the water often to prevent build up of end level non-biological materials (such as phosphates) than will accumlate. If i replicated the tank on a much larger scale (say 2000 litres) then the water changes would likely to few and far between.
Self sustaining is a point of view.
Your go Actnic!
