We only drew ocean water after a steady string of good weather. We never took water during bloom alerts or just after storms. The sand separator elements filtered down to 25 microns making parasites not much of a problem. UV and garlic kept the sharks parasite-free. Although, the occassional shorebird would deposit something that needed treatment every once in a while.
The water from Scripps Institute of Oceanography was so clean the fish looked like they were traveling through air. It was more than adequate for my leopard sharks, brown smooth hounds, guitarfish, and horn sharks. The bat ray did well in this water, too, until he was large enough to move to the pond.