Illnesses From Black Algae in a Pool

Black Algae Health Risks

• Black algae is the type of algae that clings to the walls of the pool, and will return quickly after it has been scrubbed off. This is the same kind of algae that is often referred to as mold or mildew when it forms in bathtubs and sinks; it can also be found growing in fish tanks. In itself, this algae will not cause illness even when ingested by people or animals. However, when the algae is allowed to gain a foothold in the pool that is firm enough to allow it to grow and form noticeable spots, this usually means that there is a chemical imbalance in the pool that is allowing the growth. When there isn't enough chlorine or other sanitizers in the pool to kill the algae, this usually means other types of bacteria are also beginning to grow.

Associated Bacteria

• Bacteria of all kinds can be found infecting a swimming pool that has been overrun with black algae. E. coli is a common type of bacteria, which are known for causing gastrointestinal distress and effects similar to food poisoning. Another type of bacteria, cryptosporidium, causes similar symptoms and can quickly develop in dirty pool water and improperly sanitized conditions like those that spawn black algae. Some types of bacteria, such as giardia, not only cause gastrointestinal distress in those exposed but are resistant to chlorine and other pool sanitizers. Once these types of bacteria establish themselves in the pool, it can take repeated treatments to remove them and make the water safe for swimming.

How It Happens

• The pH levels of the pool water influence how well the sanitizers are able to do their job. If the pH level is out of the acceptable range or if the levels of chlorine or bromine drop too low, not all of the invading microorganisms in the pool will be killed and removed by the water. Instead, they will begin to multiply. Once these microorganisms begin to multiply, they become harder for the sanitizer to control. The presence of black algae means that the chlorine or bromine present in the pool is not only failing to kill the algae, but it is also being used up by the process of killing algae when it should also be killing bacteria.

Making Pools Safe

• Restoring the proper balance of pH and chlorine or bromine levels in the pool is crucial. Test the water and add the amount of chemicals needed to bring the results up to acceptable levels. Black algae is a strain that is typically resistant to chlorine and weak types of algaecide such as polyquats, so add a type of algaecide that is made specifically for black algae. This will directly kill the algae microorganisms, allowing the sanitizing agents to kill the bacteria that would make swimmers sick. In order to ensure the removal of all dangerous bacteria, test the pool daily for up to a week to be sure that correct chlorine or bromine levels are being maintained. Brushing the sides of the pool with a stiff brush will loosen black algae that has taken hold and is harboring any bacteria with it.