Buffering requirements

How much buffering does your tank need? Most aquarium buffering capacity test kits actually measure KH. The larger the KH, the more resistant to pH changes your water will be. A tank´s KH should be high enough to prevent large pH swings in your tank over time. If your KH is below roughly 4.5 dH, you should pay special attention to your tank´s pH testing weekly, until you get a feel for how stable the pH is. This is especially important if you neglect to do scheduled partial water changes. The nitrogen cycle creates a tendency for an established tank´s pH to decrease over time. The exact amount of pH change depends on the quantity and rate of nitrates produced, as well as the KH. If your pH drops more than roughly two tenths of a point over a month, you should consider increasing the KH or performing more partial water changes. KH doesn´t affect fish directly, so there is no need to match fish species to a particular KH.