I would also suggest that you need at least a working understanding of alkalinity and calcium and how to maintain those levels. Ocean water has a certain balance of major and minor ions. (i.e. "salts") These salts need to be kept at the correct ratio or eventually you will have "salt water" which is not actually the equivalent of "ocean water".
Think of it this way... if you add table salt to freshwater you can get a salinity of 1.024. But this wouldn't be the saltwater that we need to maintain fish. The saltwater we need must mimic ocean water, which has certain levels of hundreds of major and minor ions, forming salts.
For this reason we use Instant Ocean or another salt mix. But even then there will be changes in these ions as acids are produced from detritus decay and organics being processed by the bacteria in the live rock and sand. The major ion in saltwater is Calcium, so even in fish only tank, you need to be concerned with alkalinity and calcium levels.
More on that here: