I use seawater in my tank that is purified at a lfs who I trust. Since I live in South Florida, it's pretty easy to get good stuff. My question is this. Since the parameters of seawater are usually a little lower than the saltwater made with salt mix, is it really the best choice? I know that mg, ca and alk are often kept at higher levels in tanks, for example. I always thought natural seawater would be best, but is this a case of science trumping nature? This is all assuming that the seawater has no pollutants, which I believe to be true. Any thoughts?