Does Too Much Calcium Affect the Freshwater Fish Tank?

High calcium levels are universally beneficial in saltwater aquariums, but high levels of calcium in a freshwater tank can be good or bad. Freshwater fish have diverse preferences for water chemistry, and you have to match your water to the fish you wish to keep.

  1. Calcium and pH

    • Dissolved calcium affects the pH of aquarium water. Dissolved minerals, including calcium buffer water. This means they interact with the water in such a way to maintain a constant pH and make the water resist changes in pH. Generally, calcium buffers water at a high pH, making the water alkaline or basic.

    Water Creep

    • Additionally, dissolved calcium contributes to water stains. Also called salt creep, lime scale and hard water stains, calcium deposits materialize when aquarium water splashes onto a surface and evaporates, leaving behind tiny minerals that were dissolved in the water. The stains tend to build up on aquarium lids and on the tank where the water line evaporates. Daily cleaning with a rag helps control calcium buildup. Water rich in dissolved calcium is more likely to form water stains that softer water.

    Effect on Fish

    • The effects on fish vary based on the species of fish. Fish that come from hard water thrive in calcium-rich water. For example, African cichlids and central American livebearers have adapted to hard, calcium-rich water; they breed and show their best colors in water with lots of dissolved calcium. However, fish from soft water, including many South American cichlids and tetras, will get stressed since they have not adapted to hard water.

    Overcoming Hard Water

    • If you have hard water and want to keep fish who come from soft water environs, you can use the process of reverse osmosis or RO to remove dissolved minerals from your tap water. Do not use water softeners, since they tend to replace dissolved calcium with other minerals like salt. RO units typically cost a lot and produce wastewater. You can use this wastewater for watering plants or other chores. RO water has very little in the way of dissolved minerals and almost no calcium.