Cloudy aquarium water is a sign that something is amiss in your tank. Maintaining good water quality is one of the most important on-going facets of maintaining a healthy tank. Cloudy aquarium water often signifies high levels of bacteria in the water. These bacteria can have a variety of causes which need to be identified and eliminated, along with the water being cleaned.

Keep in mind, when it comes to maintaining aquarium water quality, the size of the tank can make a difference. Larger aquariums are often easier to maintain, especially for beginners. Because the water must be properly treated for the fish and plants to survive, having more water allows you a wider margin of error and a more forgiving environment.

Cloudy aquarium water with a greenish tint is usually a sign of algae bloom. The most common causes for this are too many nutrients (generally phosphates and/or nitrates), and too much lighting. A high nutrient level is often caused by overfeeding your fish. The excess food falls to the bottom of the tank and decays, releasing phosphates. An excess of light, not only from the tank light but also from room lighting and too much sunlight, can also cause algae bloom. Because algae consume oxygen at night, algae bloom can quickly deplete the oxygen levels in your tank. Be sure to try to increase oxygen circulation while treating the tank, to prevent problems for your fish. Clean the tank by vacuuming the gravel, cleaning the filters, and performing a partial water change. You can also use chemicals known as flocculants, which pull together small bits of debris into larger clumps that can be filtered out. To prevent future problems, reduce the amount of food and determine whether reducing light is necessary.

Cloudy aquarium water that appears whitish is often due to a bacteria bloom. This can sometimes be caused by excess feeding, similar to an algae bloom. Another common cause of bacteria bloom is overly thorough cleaning of the filters and gravel (yes, your tank can be “too clean”). Start by reducing the amount of food you are giving your fish, to prevent overfeeding. Check ammonia levels frequently, as they can rise to a dangerous level during a bacteria bloom. As with an algae bloom, using flocculants can help clear the tank.

Cloudy aquarium water signals an unhealthy environment for your fish. Regular water changes can help prevent these problems. Change 2 to 5% of the water in the aquarium weekly, if needed. Changing less than this will not generally have enough positive impact to be worthwhile; changing more than this can be detrimental to the aquarium. If you do not perform small water changes weekly, a monthly water change should be done. If done monthly, this change should be around 15% of the water in the aquarium. Changing the water helps remove chemicals that are not filtered out, and helps to keep the gravel clean. Cloudy aquarium water signals a problem, but it need not be cause for alarm. When identified and treated properly, your cloudy aquarium water can be crystal clear again in no time.