Media is anything used as a platform to house roots. From inert rocks to living soils. Amended and living soils have nutrients in the soil. Only water is required. The life in the soil makes the nutrients soluble in water. If the soil/growing media is not amended with nutrients, nutrients must be delivered to the media/roots in water. Most bag soils like Fox Farm are lightly amended with about a month or so of nutrition, some have non. After that runs out, you’ll need to use a bottled or powdered nutrient formula. That’s the situation you’re finding yourself in. You’ll need to start supplying a liquid nutrition solution soon.