High nitrate levels can encourage excessive algae growth, which can make the aquarium look unsightly. Unlike other nitrate reducing products, which need regular recharging and replacing, Tetra NitrateMinus is simply added weekly to the aquarium. Also unlike many ordinary nitrate reducing products, NitrateMinus does not need to be added to a filter system to work, but is simply added straight to the water. How it Works: NitrateMinus utilises a natural biological process called de-nitrification to remove nitrate. Under conditions of low oxygen, such as are found under the gravel in most aquariums, special bacteria use nitrate instead of oxygen to break down the NitrateMinus granules. By doing so, they steadily reduce existing nitrate levels, and maintain a permanently low level. In addition to removing nitrates, NitrateMinus also releases a low level of carbonates into the water, which helps to stabilise the pH of the water. How to Use: Simply add 2.5ml/10 litres of NitrateMinus to the aquarium once a week to keep nitrate levels low. NitrateMinus must be in an oxygen poor environment to work. The effectiveness of NitrateMinus may therefore be reduced in aquariums with under-gravel filters.