How long the nutrients in Black Earth Premium last depends on the rate of plant growth inside your aquarium. If you have a low-light, no CO2 tank where plant growth is relatively slow, the nutrients within the substrate can last a year or more. However, if you run a high-light tank with demanding plants and CO2 injection, nutrient release from the substrate may not keep up with the demand. As a result, additional fertilizers may be required after several months of plant growth. Because of this, we highly recommend using Green Base XR, Substrex, and Multi-R below the soil layer to maximize substrate nutrients from the beginning.