Setting up a marine aquarium is the final point of aquarist because it seems difficult and demanding. Its not same with growing a freshwater fish up. You have to pay attention a lot of different parameters of water and arrange it everytime. Many inaccurate legends have been generated about how difficult saltwater aquariums are to keep. Top Saltwater Aquarium Myths details explains why they are inaccurate. A freshwater aquarium is a bit simpler to set up and maintain than a saltwater aquarium. However, if the most common mistakes are avoided, they are really not all that difficult. The main aim is to provide same ratio of seawater, by this way all of vertebrates and invertebrates which you want to grow up can live normally. If any aquarist can do all of them, after a while, everything is going on very-well because marine aquarium system clears oneself but anyhow you have to control the system ratio.
First of all, City Mains Water is not good enough to grow live up. It have to be cleaned by special water purifying equipment. The two most common systems used are de-ionization resins and reverse osmosis membranes. Anyway, you can buy that everywhere.
Marine aquariums have two part. First one is tank in which you will grow your vertebrates or invertebrates,corals up and other one is sump is required to provide biological filtration and clean our system. You have three kind of filtration but the most healthy is biological. Others are chemical filtration, mechanical filtration (if you dont clean filters of mechanical filtration, after a while to be hold particulates rot and it makes dirty your aquarium).
It means,
Biological filtration is required to keep living.
Chemical filtration is important to throw chemical harmful.
Mechanical filtration is required to collect protein and nitrates .
First of all you should decide which type of system you want. if your dream