Agreed. If you add the water whilst everything in it is still alive you are adding fresh food, which is good (although you could also be adding living parasites, which could be harmful...). If you allow the water to "age" then everything which has died will "pollute" the water, even if it has "cycled", as the end nutrients (phosphate, nitrate, silicate, etc.) are NOT removed.
Living in Bloem, I don't have any choice but to use artificial salts, but I will choose NSW collected from an unpolluted beach over any salt mix if I had a choice. The problem with Two Oceans water is that it is sourced from the harbor, which is more polluted AND has a large salinity swing (whenever the Cape has heavy rains the water runs off into the harbor and the SG drops...).
Hennie