Are Calcium Ions Dangerous to Fish?

Fish from different locales have differing water chemistry preferences; put one in the wrong water and you'll kill him. Among many other things, calcium ions are among the elements that make up water chemistry. For some fish, water rich in calcium is a good thing; for others it's not. You need to know the exact ideal water parameters for each fish you keep. However, you need to test for calcium directly only in reef tanks.

  1. Calcium Ions

    • Calcium ion levels relate to other aspects of aquarium water chemistry.

      Calcium appears in tap water and in the home waters of many fish. It usually enters water from dissolved mineral sources. For example, the Rift Valley Lakes in eastern Africa are carved out of calcium-rich bedrock, so the water has plenty of calcium in it. Calcium ions have an effect on a number of other aspects of water chemistry. For example, calcium ions raise the pH, alkalinity and hardness of water. Specifically, calcium ions make water less acidic, more alkaline and harder.

    Lowering Calcium Ion Levels

    • Use driftwood from a pet shop to avoid contamination.

      Many popular aquarium fish come from rivers and lakes with very low levels of calcium ions. For example, much of the Amazon drainage is fed by pure rainwater and runs over relatively inert bedrock. Many fish from this and similar areas need soft, acidic water to thrive in the home aquarium. To lower the amount of calcium ions in water, you can purify the water through a process called reverse osmosis or RO. RO water has almost no dissolved calcium ions. You can use this water to dilute regular dechlorinated tap water to lower the levels of calcium, as well as the pH and hardness, for fish who need such water.

    Raising Calcium Ion Levels

    • Limestone slowly leaches calcium and other minerals into aquarium water.

      Some fish, like African cichlids and saltwater fish, need water rich in calcium. To raise the calcium ion levels -- along with the pH, alkalinity and hardness -- you can add the mineral a number of ways. You can passively raise the levels by using decorations like crushed coral sand and tufa rock, which slowly dissolve in aquarium water, leaching out calcium and similar minerals. You can also increase calcium levels with liquid supplements, though many have negative effects on other aspects of water chemistry if used carelessly. Calcium reactors are another option. When used correctly, they do not affect other water parameters as much. However, calcium reactors are expensive and tricky to set up.

    Testing and Desired Levels

    • Corals use calcium to build support structures.

      In most fish tanks, you do not have to test the level of calcium ions. This is because the effects of calcium ions show up in other areas of water chemistry, like pH and hardness. However, if you have a reef tank -- a saltwater aquarium featuring coral and other invertebrates -- you should test for calcium. These organisms constantly absorb calcium from the water to make the hard structures in their body. You should test a reef aquarium at least monthly for calcium ion levels. Ideally, the calcium ion levels should be 380 to 459 mg/L.