Cover the bottom of the aquarium with a 1.5 cm deep layer of HUMUS, avoid packing it down and then cover with a 6-7 cm deep layer of gravel. This product maintains its efficiency for a long period of time (approximately 2 years) and should be replaced at each new aquarium set up. Caution: before filling the tank with water, it is recommended to cover the gravel with a nylon sheet to avoid that the jets of water move the soil below. It is possible that the water initially will turn a pale amber colour, this is due to the humic acid content of the HUMUS peat. It is not a PPP (plant protection product). This is not a fertilizer.