Phosphorus 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 nourishing system. Flourish Phosphorus is a safe solution of potassium phosphate that takes the guess work out 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. Likewise, because Flourish Nitrogen is phosphate free you can use both products together to target exactly the ideal amounts of each for your system. 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.