How it works
A water change dilutes nitrate. Changing half the water with nitrate-free tap water halves the nitrate. If your tap water already contains nitrate, each change does less, and you can never go below the tap level.
Most tanks do well on 25 to 30 percent a week. Use this calculator when a test shows nitrate has climbed and you want to know how much it takes to fix.
Test your tap water once, so you know what you are starting with.