Seachem Flourish Phosphorus for Planted Aquarium has phosphorus which is one of the main three macro nutrients (nitrogen, phosphorous, potassium: NPK) required by plants and can often become the limiting factor to growth in a flourishing system. Flourish Phosphorus is a safe solution (4500 mg/L phosphate) of potassium phosphate that takes the guesswork out of phosphate dosing. Unlike competing products that mix nitrate and phosphate in a fixed ratio, Flourish Phosphorus (being nitrate free) allows you to dose phosphorus according to the needs of your plants without the risk of overdosing nitrates. When used as directed, Flourish Phosphorus will enhance and accelerate the growth of aquatic plants without enhancing algae growth. For maximum benefit, use with Flourish Nitrogen and Flourish Potassium. Flourish Phosphorus is safe for invertebrates such as shrimp.