A little more info would be helpful. How big is the tank? What was in it? How long had it been set up? What filter was being used? Do you have any test kits to check pH, ammonia, nitrites and nitrates? These would give us a better idea of what has happened.
Usually white water means an imbalance in the tank and so you get the white, temporary, algae bloom which clears itself. It is also harmless to fish.