General hardness (GH) in aquariums refers to the concentration of dissolved minerals, primarily calcium and magnesium ions, in the water. Elevated levels of these minerals can create an environment unsuitable for certain fish and plants that thrive in softer water conditions. The process of decreasing GH involves reducing the concentration of these dissolved minerals, thereby softening the water. An example includes using reverse osmosis (RO) water, which is essentially free of minerals, and then blending it with tap water to achieve the desired GH level.
Maintaining appropriate GH levels is crucial for the health and well-being of aquatic inhabitants. High GH can lead to stress, stunted growth, and even death in sensitive species. Moreover, excessive mineral content can inhibit the absorption of essential nutrients by plants. Historically, aquarists have employed various methods to manage water hardness, ranging from simple water changes with naturally soft water sources to more sophisticated filtration techniques.