How Long Will My Aquarium Stay Cloudy?

Cloudiness in your new aquarium is a reassuring sign that bacterial populations are starting to colonize the tank, but cloudy water in an established tank can indicate problems with excess nutrients, algae, dust or debris. Bacterial blooms in new aquariums last from one day to two weeks, but usually sort themselves out eventually. Cloudiness in established tanks won't disappear until water quality improves.

  1. Blooming Bacteria

    • Beneficial bacteria are essential in a healthy aquarium, but too many bacteria turn water cloudy. When setting up a new tank, bacteria numbers build up in the water before beneficial bacteria populate the gravel, forming a biological filter for harmful chemicals, such as ammonia. When bacterial populations stabilize the water turns clear, often overnight. Increasing the depth of gravel to 3 inches can help if bacteria have insufficient surface area to colonize. In an established aquarium, bacterial populations grow out of control when there are excessive nutrients in the water, which is often caused by overfeeding fish. Feed fish very small amounts two or three times a day, and remove uneaten food from the tank. Adding chemicals to control cloudiness caused by bacteria rarely provides a long-term solution.

    Green Menace

    • Cloudy green water is a sign of algae, which are tiny green organisms that form a slimy coating on walls and decorations in a healthy tank, but can also float freely in water. Algae need sunlight and nutrients to grow, so move your aquarium out of direct light and feed your fish less. Add aquatic plants to your tank to help starve algae of nutrients, and install a mechanical filter to remove them from the water. UV filters also help reduce algal growth. Algacides kill algae but can damage biological filters and harm fish health.

    Dust Cloud

    • Introducing decorations or fresh water, or failing to change water frequently enough, can all cause cloudiness in an aquarium. Dust from aquarium decorations turns water cloudy, so rinse new decorations thoroughly under cool running water before putting them in your tank. Check items in the water for signs of dissolving or flaking and remove anything that looks suspicious. Buy aquarium decorations only from reputable pet stores. Adding fresh water to an aquarium causes temporary cloudiness, but not adding water allows debris from rotting food, fish feces and plants to build up and cause cloudiness that increases over time.

    Cleanliness, not Cloudiness

    • Regular, small water changes improve cloudiness in an established aquarium and help prevent it returning. Remove 10 to 15 percent of the water with a filtered siphon, and replace it with water treated with a chlorine remover, once a week. At the same time, remove debris with a net or siphon, paying special attention to the gravel -- a blocked undergravel filter increases cloudiness in aquarium water. Remove decorations and wash them in cool, clean water, and scrape algae from the sides of the tank with a soft plastic scraper. Don't use soap, detergent or other cleaning products to clean aquariums.