EBaySeachem Flourish Phosphorus 1 Gallon.  Flourish Phosphorus 4 Liters (1.1 Gal) Flourish Phosphorus is a safe solution (4500 mg/L phosphate) of potassium phosphate that takes the guess work 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. Why It Is Different? Unlike competing products, Flourish Phosphorus is entirely nitrogen-free, making it possible to adjust the Phosphorus level in an aquarium without affecting nitrogen levels. Directions BEGINNER: Use 2.5 ML (half a cap) for each 80 L (20 gallons*) once or twice a week or as needed in response to signs of phosphorus deficiency (e. G. Stunted growth, plant dark green). EXPERT: The beginner dose raises phosphorus by 0.05 Mg/L (0.15 Mg/L phosphate). The ideal phosphate level will vary, but generally ranges from 0.15 To 1.0 Mg/L.  Use MultiTest: Phosphate to monitor phosphate levels.  To target a specific phosphate increase, dose according to the following formula: 0.8Vp=m, where v= volume of tank in gallons*, p=desired phosphate increase and m=volume of product to use in mL. For example to raise 20 gallons* to 0.1 Mg/L phosphate you would use: 0.8*20*0.1=1.6 ML Condition is New. Shipped with USPS Ground Advantage.