The water quality of tap water varies by area. There are a few parameters on tap water having a big impact on the growth of aquatic plants and fish keeping, namely pH (hydrogen ion concentration), KH (carbonate hardness) and TH (total hardness). These three water quality parameters are interrelated and if tap water is high in pH (i.e., water is alkaline), its KH and TH also tend to be high. On the contrary, tap water with low pH (i.e., acidic water) tends to have low KH and TH levels. Under the regulation concerning drinking water in Japan, the pH level of tap water must be between 5.8 and 8.6, covering a broad range from acidic to alkaline water. In Japan, the common pH level of tap water is between 7.0 and 7.5 nationwide. However, the tap water in some areas shows a pH level as high as 8.0. In alkaline water with a high pH level, the photosynthesis of aquatic plants is affected and their growth is interrupted. Besides, most tropical fish prefer mildly acidic water and they cannot display their beautiful colours in alkaline water. Aquariums having Aqua Soil substrate experience a decline in pH and KH in the initial setup phase because Aqua Soil is made of natural soil that is acidic. If your tap water is alkaline, the soil’s acidity will eventually be neutralized by adding the tap water into the tank through water changes. Soft Water, a new addition to the Aqua Conditioner lineup, lowers pH and KH of water to make the tap water closer to mildly acidic water conducive to many aquatic plants and tropical fish. Soft Water also helps maintain the acidic property of Aqua Soil for a longer time. For your information, if the tap water of your area is alkaline, Aqua Soil-Amazonia Light, which is more acidic than normal Amazonia, is a better choice for substrate material. To maintain mildly acidic water suitable for Nature Aquarium for a long time, it is recommended to use Green Brighty Neutral K for replenishment of potassium and apply Soft Water to the tap water used for a water change.