Why Did My Aquarium Water Turn White? What to Do

Milky water is usually biological (from overfeeding, unsterilized live food, or poor cleaning letting protozoa boom) or limestone turbidity (from unwashed gravel shedding lime). It clouds the tank, presses out beneficial nitrifying bacteria, stresses fish, and can smell. Fix it by more frequent water changes and cleaning, a UV sterilizer, stronger filter media, added beneficial and nitrifying bacteria or enzymes, and for lime, dilute with water changes, use potassium fertilizer, or add a clarifier and siphon the settled matter.