05-27-2010, 01:59 PM
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Two different but related issues here. First on the bacteria.
Nitrosomonas and nitrospira bacteria require "food" in the form of ammonia and nitrite respectively. When bacteria that have colonized filter media, wood, rock, substrate, plants, decor--any hard surface in fact--are transferred to a "new" tank, they can last several hours before they will die off if there is no source of ammonia such as from fish. Nitrosomonas bacteria at optimum temperature and pH will multiply by binary division in about 9 hours; each bacterium divides into two new bacteria, called binary division. Provided there is a source of ammonia to trigger this, it will continue. Same for the nitrospira only some authors say this can take up to 20 hours for binary division.
The issue here is obviously having sufficient bacteria transferred to handle the ammonia from the fish. As this is unlikely for several hours, aquarists recommend very few fish in a "seeded" new tank to allow sufficient time for the bacteria to catch up. Ammonia and nitrite are highly toxic to all life, fish and plants, so it is important to ensure sufficient bacteria are present for the fish load.
However, we here come to the second related issue, plants. Live plants will immediately "cycle" a new tank. Plants use ammonium as their preferred source of nitrogen, an essential macro-nutrient. Fish and bacteria in the substrate constantly produce ammonia as a by-product, and in acidic water this changes to ammonium. The plants grab a lot of it, and use it; they are actually faster at doing this than nitrosomonas bacteria, which is why in a heavily-planted aquarium the level of nitrifying bacteria is quite low by comparison to one without plants. In basic water, the plants have the ability to internally convert the ammonia to ammonium which they then assimilate.
Provided you have sufficient plants to balance the fish load, you can add the fish all on the first day (with the plants planted) and there will be no "cycle" as such. I have set up dozens of tanks this way, as have many others. This plus the seeding from existing filter media (still a good idea) will work fine.