Light gravel is a neutral substrate which highlights darker background & decorations in your aquarium. Instructions: Rinse until the water runs clear before adding the gravel to the aquarium. The waterscape will look more natural & create a feeling of distance if the gravel is higher at the back of the aquarium & slopes gently away towards the front. We recommend using a nutrient rich substrate mixture as a base layer to encourage healthy plant growth & to help maintain correct p H levels. To view our full range of Aquarium substrates, please click here: Aquarium Substrates Amount needed for approx. 5 cm layer in a rectangular aquarium: Dimensions: 60 x 30 cm approx. 15kg Dimensions: 80 x 35 cm approx. 25kg Dimensions: 100 x 40 cm approx. 35kg Dimensions: 120 x 40 cm approx. 40kg