What makes saltwater aquariums so different to freshwater aquariums

Saltwater tanks are harder due to PH and ammonium!
Salt water with calcium, magnesium and so on in it turns the ammonium to ammonia; the higher PH does this, ammonia is far more toxic then ammonium!
In freshwater it is really only ammonium that exists in there due to lower PH, unless you keep your PH above 7.8, then your waters will begin to hold ammonia and not so much the more harmless ammonium!
When we saltwater hobbyists neutralise ammonia to protect our guys when there is an event of a bad kind happening, we add chemicals that turn ammonia to ammonium during that time!
I use ammo lock!