Eightball...
This is a rather large question, but I'm glad you've asked it! I'm a little confused, since I see that you have posted 30 times... Sorry if any of the info below is obvious...
I'll give you an overview, but you really need to research "cycling a tank" on the internet. This is not difficult to find, and I think you'll see that there are some excellent resources out there.
"Cycling" describes the establishment and progression of the Nitrogen cycle, a cycle which happens in nature as well as in tanks. In the cycle, Ammonia (
NH3 or
NH4+), a poisonous substance produced in fish waste and by decaying food, is broken down by 1 species of bacteria to Nitrite (
NO3). Nitrite, in turn, is broken down by a second species of bacteria into Nitrate (
NO2). Nitrate is broken down by a third species of bacteria into gaseous Nitrogen (N2). This gas may now leave the tank.
The three species of bacteria need to be established in your tank. Luckily they exist in small amounts in water, so they will grow in numbers as fish waste builds up. BUT, because they are starting from nought, these bacteria are not populous enough to deal with all the produced ammonia, nitrite and nitrate. As a result, a new tank will have an ammonia spike, during which ammonia levels surge to over 8
ppm (it's poisonous to most fish at levels over 0.5
ppm!). When this ammonia is finally consumed, the level should drop to 0
ppm, and the Nitrite levels should soar to over 8
ppm. These then fall, and the Nitrate levels should even out at around or below 30
ppm. At this point, the bacteria and fish waste is in equilibrium, and fish can live safely in the tank.
Many people say that the full cycle with fish (usually zebra danios) takes about 2 weeks. With larger tanks, this often takes even longer--7 weeks is usually quoted. If you wish not to cycle your tank, you can buy Bio-Spira instead, which you drop into the tank just before you put your fish in. Bio Spira is a combination of the three types of bacteria I mentioned before, and should immediately combat the ammonia/nitrite/nitrate produced by fish. If, however, Bio Spira is placed in the tank, and fish are not, the bacteria will starve, and will quickly die. Why not use Bio-Spira? It's expensive, sensitive and hard to come by. It must be kept frozen so that the bacteria don't die. But it works, and it works fast.
Just so you know, this is what people mean by "biological filtration." In any tank the three types of filtration must exist. Mechanical filtration physically blocks large pieces of waste from re-entering the tank (the sponge), chemical filtration (the carbon) neutralizes several dangerous compounds and biological filtration (bacteria) converts poisonous compounds to harmless ones. It's a fantastic concept, and if you keep tank conditions relatively consistent and steady, the bacteria will thrive in your tank, and the nitrogenous compounds won't increase. Of course, water changes are still important, as they pretty much guarantee that levels of these compounds won't build up too much if the system isn't in perfect equilibrium.
Lack of knowledge about the cycle is the #1 killer of new fish. A poorly established Nitrogen Cycle is the reason for “new tank syndrome” during which all the fish in a tank may die over a period of 2 or 3 weeks. If you didn’t know before and you know now, count yourself lucky!
Sorry if I've misunderstood your question...
I could tell you about plants, too, but I've written a lot already. PM if you want advice on lighting etc.
