Brightwell Aquatics Magnesion - Liquid Magnesium Supplement for Reef Aquaria 500ml / 17oz Highly-concentrated ionic magnesium solution. Provides magnesium, which helps regulate the balance between calcium and carbonates in aquarium wate Stronger than most competing products. Contains no unwanted organic material such as EDTA, gluconate, or polygluconate. Formulated by a marine scientist.