well,to start with,saltwater,either collected from the ocean or salt mix from a petshop(not normal table salt or rocksalt)and mixed with RO water.
RO water is water that has been passed through a reverse osmosis unit to remove any impurities.
For topping up your aquarium water(as fresh water evaporates,I lose 4-7 liters per day)you would use RO water also.
saltwater
Not all sharks live in one type of water. Most of them live in saltwater but the bull shark can live in both saltwater and freshwater.
I can answer your question without you having to search and search. The good rule of thumb for freshwater is one inch of fish for every one gallon, but goldfish and saltwater are different. Goldfish need 3 gallons of water to every inch of fish, same goes for saltwater.
Saltwater.
Seaweed, by its very name, comes from the sea, and is thus saltwater.
The temperature of the water depends on the type of life/fish you intend to keep in the aquarium.
It depends on the type/brand of conditioner, and how much water is the Betta tank can hold.
It depends on how many fish you have in the tank and the type of filtration you have. If the tank is heavily stocked then the water should be partially changed every week - around 10-15% is fine.
It varies, but usually the rivers freshwater mixing into saltwater.
Most all sharks live in saltwater except the bull shark which can live in freshwater and saltwater.
Saltwater is a mixture of solid and liquid molecules. Once the salt dissolves, the substance becomes a solution.
saltwater the category even says it!