HLLE in an ocean surgeonfish (Acanthurus bahianus) caused by the use of activated carbon. Many different factors have been considered as possible causes of the disease known as Head and Lateral Line Erosion (HLLE)—a condition that typically causes disfiguring tissue erosion on the head and along the sensory lateral line of certain marine fishes. Poor water quality, nutritional deficiencies, protozoa of the genus Hexamita, stray voltage, and activated carbon use are just some of the potential causes that have been floated over the years. However, as Jay Hemdal explains in the following excerpt from his new eBook, The Salt Smart Guide to Preventing, Diagnosing, and Treating Diseases of Marine Fishes, there is now some solid scientific backing to the notion that activated carbon can cause this condition. From Chapter 3: Husbandry, Environment, and Your Fishes’ Health “A relationship between the use of activated carbon in aquariums and the development of HLLE in surgeonfish has been positively shown in two scientific studies. Other than that, no formal studies have been undertaken that identify other causes. However, a multitude of unproven causes have been presented by various people. Commonly, stray electrical currents and vitamin deficiencies are cited as causes, but one of the studies mentioned above ruled these out as common causes
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