Alloy selection is critical for proper protection. Zinc is recommended for use in salt water (not recommended for fresh water). Aluminum is designed for use in salt or brackish water and has better performance and longer-lasting protection than zinc. Magnesium is intended ONLY for use in fresh water and is the only alloy proven to provide protection in fresh water. Martyr brand marine anodes are a subsidiary of Canadian Metal (Pacific). Using advanced alloys and casting Martyr brand sacrifical anodes have gained an international reputation of superior quality.