Nutrient capsules contain nitrogen, phosphorus, iron, and micronutrients. The nutrients are released slowly as the plants need them. Use Nutrition Capsules for stem plants, Cryptocoryne, Echinodorus, Vallisneria, etc. - all plants with strong roots. Nutrition Capsules are an additional nutrient supplement - place the capsule in the gravel near the roots of fast-growing plants using tweezers.