Why does my fresh mixed salt water have a really low ORP? My tank runns at about 400. When I add fresh saltwater to the tank, it drops to about 270? Is it because of low oxygen content in the freah mixed water since it is not airated? It is mixed in a closed barrel, but the pump does agitate the surface. Seems odd that the balance of oxidizing agents and reducing agents would be that much different in the tank than the fresh salt water. Maybe I should try airating it for a while and see if that brings it up.