Ok, I think I understand your question, and while the question itself makes sense now, the "subject content" does not.
The nitrogen cycle is something that happens in every tank, you can't avoid it, and it can be very dangerous if it isn't stable.... for fish, inverts, anything living in the tank.
The nitrogen cycle is the course of good bacteria building up in the tank to break down the waste products in the tank to a safer form. This is where water testing becomes so important. While every tank will go through this "cycling" process, some do it faster than others, and it's important to know that the first stages of the cycle are known to be toxic to the animals (fish as well as inverts).
An average saltwater tank will take approximately 6 - 8 wks to cycle. During this time ammonia will peak to a toxic level. As the good bacteria begins to grow, it feeds on the ammonia, which breaks it down. The waste product from the bacteria eating the ammonia is then called nitrite. More bacteria will feed on the nitrite, and break it down, thus creating nitrate as the waste product. In fresh water, the only way to remove nitrate is with water changes and live plants to help eat the nitrates. (Nitrates in freshwater is plant fertilizer). In saltwater, howerver, there are more bacteria that will eventually break down "some" of the nitrate level as well.
Ammonia, nitrite, and nitrates in a high level are all toxic to fish and inverts.
When beginning a new saltwater tank, there are basic steps that need to be taken before adding any animals to the tank.
1. add water
2. add salt until specific gravity/salinity (spg) are 1.023 (this will usually take a few days to mix completely for an accurate reading) This is also a good time to add the heater and set it for 76 degrees
3. once spg is where it should be at 1.023, and temp is stable at 76, then we add live sand and live rock (in most cases). The small organisms and bacteria in the live sand and live rock will help to get your cycle started.
4. patience... wait... test water for ammonia, nitrite, nitrate, pH, calcium until everything is stable where it should be, which is ammonia at 0, nitrite at 0, nitrate should be low, 20 or less... pH is safe between 8.2 - 8.5 for saltwater, calcium should be between 400 - 500
5. small water change to help relieve any nitrate buildup
6. add first animal(s), only 1 - 2 at a time, especially in a smaller tank (55 gallons or less)
7. wait at least 2 wks before adding next animals, with a small water change in between
It is always suggested to use live rock in a saltwater tank. Live rock is where much of your bacteria culture will grow. Without it, or some type of porous rock that can be cured over time and turned into live rock... the bacteria then only has the sandbed to grow in, which is not usually sufficient enough to sustain a saltwater tank long term. Live rock in the amount of 1 lb per gallon (or as close to it as you can get) of the tank is the reccomended quantity
If you use a bacteria starter, such as "biozyme", the bateria still needs to culture and grow in the tank before adding the fish.
When working with live rock it is important to know that the changes in conditions and the level of curring it has had will determine the amount of "die off" it produces, but anything that was previously on the rock such as algae and other matter will begin to break down, which then turns to ammonia and must go through the nitrogen cycle process to properly break down and become safe and stable. This is the reason I always suggest waiting at least a few wks and doing testing during this time before adding fish.
Saltwater isn't really any harder than freshwater, but it will usually take more time and require more patience and attention on your part to become and remain stable..
Does this help?