How to Keep Magnesium Up in an Aquarium

Whether man-made or natural, saltwater loses elements after circulating through a reef tank. Essential ions and trace minerals, including magnesium, get absorbed by corals and other invertebrates, or get swallowed in the protein skimmer. Magnesium is necessary to the health of corals and also helps maintain calcium and alkalinity balance in saltwater aquariums. Therefore, an aquarist must replenish lost magnesium.

Things You'll Need

  • Magnesium testing kit
  • Gravel vacuum
  • Man-made or natural saltwater
  • Chemical additive containing magnesium
  • Aragonite sand
Show More

Instructions

    • 1

      Measure your reef tank's magnesium levels. Aquarium and pet stores sell a variety of kits to test for magnesium and other elements. Follow the manufacturer's instructions to obtain an accurate reading. According to the article "Aquarium Chemistry: Magnesium in Reef Aquaria" on the Advanced Aquarist website, you should target natural seawater concentration, which is 1,250 to 1,350 parts per million.

    • 2

      Perform consistent water changes. The rule of thumb with saltwater aquariums is to change no more than 30 percent of total water volume every other week, vacuuming gravel well to remove waste and decaying organic matter.

    • 3

      Add a chemical additive containing magnesium. A variety of additives sold by pet and aquarium stores keep your magnesium levels optimal. Follow the manufacturer's instructions.

    • 4

      Add aragonite sand, available in most pet or aquarium stores, to your filter or substrate.