Hello; I have answered this question before maybe in more detail so if you check around there may be more information. A saltwater tank is more expensive because: 1. The salt mixture is expensive. 2. The fish are generally more expensive. 3. If frequent water changes are not done the testing of the water is more expensive. Some test kits are very expensive compared to fresh water. A saltwater tank can be set up exactly like a freshwater tank without special (aragonite) substrate or filters and will run fine. I have done this many times when I have needed more space for my marine animals. I have not noticed a need for more additives to keep the calcium, alkalinity, or magnesium at the proper levels. ( sometimes I debate the need for the expensive substrate) If a person changes the saltwater frequently (average 5% a week) the need for test equipment may be debated. As the tank grows coralline algae and animals are added that consume the elements (calcium, carbonate, magnesium) the need for water monitoring is needed. A saltwater tank and freshwater tank use the same bacteria and convert the waste into nitrate exactly the same as in freshwater. So, the same filtering equipment can be used. With a light fish load and some marine decor along with a pleasing light source ( Use good lighting and do not use aquarium plant lights as they emit too much of their spectrum in the red and blue wavelengths and tend to grow algae) a wonderful saltwater tank can be setup. Enjoy! OFM