Aquarium Water Hardness

The dH (degree of hardness) is simply the amount of dissolved mineral salts in the aquarium water. You can check the hardness of your tap water with a simple aquarium test kit. Bettas prefer soft water with a dH of less than 25. One way to dilute hardness is to add distilled water from the grocery store. Reverse osmosis units will also reduce hardness, but they are expensive and use a lot of tap water to produce a small amount of mineral-free water. Consider using one only if you need to soften a lot of water.