Why Did My Pool Water Turn Blue?

Algae Growth

• Some types of algae growth can make swimming pool water turn a cloudy, blue-green color. Blue-green algae is the most common culprit, and while the many varieties of the algae can turn the water numerous colors, blue-green water is a common sight. One of the sure signs that algae is the problem is that the pool's sides and bottom develop a slippery, slimy feeling, which can be more noticeable in areas of the pool that are regularly in the shade. Algae grows extremely quickly, and blooms can happen seemingly overnight. There may also be patches of algae spotting the sides of the pool, and these patches can be more noticeable clinging to white plastic, such as structures around ladders and lights.

Mineral Deposits

• Minerals can enter pool water from a variety of sources, and when minerals such as copper and cobalt build up in the pool, the water can turn a deep blue. Copper buildup can come from the application of several rounds of algaecides, as many algaecides use copper as one of the main ingredients. Common in older pools, copper can also be deposited in the pool when old fixtures and pipes begin to corrode, releasing the metal into the water. Cobalt can be released from fiberglass pools shells and is a less common culprit than copper.

Stabilizing the Water

• To get rid of algae, test the pool water to confirm that chlorine, pH and other chemicals are all present in the proper quantities. In some cases, it may be necessary to shock the pool to begin to get the water up to normal levels, especially after severe weather or long periods of neglect. Add algaecides designed specifically for blue-green algae to help the chlorine or bromine in the pool get rid of the algae, and flush the filtration system to make sure the organisms are not getting recycled back into the pool. Adding sequestering agents helps prevent copper buildup from collecting from the algaecides; these are the same sequestering agents that can be added to adjust the color and mineral content, if that is the core problem turning the water blue.

Preventative Maintenance

• If copper and other mineral deposits continue to be a problem, it may be necessary to replace some of the pipes and filtration systems of the pool, especially if it is an older model. Metals that come from well water can be treated with the regular addition of sequestering agents. Test the pool on a regular basis to ensure that the chlorine or bromine levels are always high enough; bromine pools need to be checked more often, as these levels will fluctuate more. Removing all debris that falls into the pool can help keep foreign bodies to a minimum, and shocking the pool after exposure to nearby fertilizers can help rid the pool of excess nitrogen that would otherwise encourage algae growth.