[Yarr]

IMO there seems ot be no short term ill effects using naturally collected seawater. however, id suggest that any toxins and whatnot that may be present in the water. ie. toxins. detergants. fuels. chemical., pesticides etc.. will take time to accumulate in quantities large enough to affect your tank inhabitant. Thus causing a massive loss.

My LFS uses natural sea water in his tanks but i do not use it. I mix my own for the simple reason i can control exactly what goes into my tank. If i didn tcare about that id just use tap water for topups iunstead of RO/DI.