I will also say that synthetic sea water is quite abnormal in many of its concentrations of compounds, far in excess of "natural" seawater, so it is a bit premature to consider it superior on all counts with natural seawater "polluted". In addition, failure of many animals, such as most seastars, to thrive in synthetic salts is in theory tied to their inability to adapt to the extreme concentrations of some compounds relative to natural seawater.
If I could easily get a "blue water" supply, even off Galveston, I would definitely do it. The area is murky due to the high sediment load carried by the bayous into the ocean - perfectly natural, BTW - so that is where settling or filtering may come in. It is also, effectively, a "QT" for the water if it is a concern. But I would happily HAPPILY use it.
Corals do quite well, even in the GOM (flower garden banks, for example). Mother nature really does have this sort of covered, and covered better than stuff we can come up with. Natural seawater is always used as the control in studies comparing synthetic salt mixes. Not the other way around. In Borneman's recent salt study, the control seawater was taken from the flower garden banks, off Texas.