Water Hardness

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Fish - Aquarium Maintenance

Water Hardness

The hardness of water is defined by the amount of dissolved mineral in the water. Hard water has high levels of dissolved minerals and is usually high in pH (pH above 7). Soft water has low levels of dissolved minerals and is usually low in pH (pH below 7). In soft water, pH levels can change rapidly but pH levels in hard water tend to be more stable.

Each species has its own water hardness tolerances; we recommend that you consult a book or other resource to determine the correct water hardness for your fish. If you need to change your pH as a result of the water hardness or if you would like to change the hardness of your water, there are commercial products on the market for this purpose. When adding buffers or water softeners, you will need to monitor the pH level to make sure it is not fluctuating too much. Consult a PETCO aquatic specialist for guidance in treating your water.

Be aware that some decorations, such as coral or rocks, could affect the hardness or softness of the water. Coral, for instance, is not good for soft-water aquariums because it contain high amounts of calcium carbonate.