Water Hardness Products
Aquarium water hardness is generally regulated by products containing calcium carbonate. Once dissolved the calcium ions will increase the dissolved mineral level and increase the pH.
Coral sand and oyster shells are used to constantly buffer these levels in the aquarium. As water passes over the surface calcium is liberated and the result is hard water. Coral sand or oyster shells can also be added to a box filter or other suitable aquarium filter.
When setting up a new fish tank or doing water changes more refined calcium carbonate is used. Hardness powders or liquid 'milks' are added to the new water and may take sometime to dissolve. By following the manufacturer's instructions the pH and hardness will be raised in a way that lasts longer than the use of a pH only product.
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Aquarium Water Hardness Reading
Aquarium Hardness Guide | Aquarium Water Guide