If you hope to start a saltwater tank based on a bunch of answers at yahoo, you are going to fail.
Places like this are meant to ask question that come up after you do your own research, it is not meant to teach you about a hobby that thick books are written about.
No, what you need to do is go and buy yourself a good book on it. The cost of it, compared to setting up a marine tank, is insignificant. If you can't afford it, you can't afford to set up this tank. Read it before starting anything. A really good fish keeper, one who has been in the game for a while, tends to have several books on their shelves - about tanks, about specific fish and livestock. I even have one dedicated to nothing but understanding fish behaviour.
Google is also your friend. There is lots of information on the web for you. It's important to check multiple sources, not just one. You might find conflicting information. Sometimes this is because people speak out of ignorance. Sometimes it's because there is more than one way to tackle things.
So that might be an example of why you come here to ask a question, to clarify something you are not sure about that you have already learned on your own.
No matter how hard people here try to answer this question and how good an answer might be, they will only cover the tip of the iceberg and you will not learn all you need to know.
Good luck.
