(NSI by Zeptometrix) A 500 mL ready-to-use standard for determination of Simple Nutrients. The sample includes: Ammonia as N 1.0 - 20 mg/L, Orthophosphate as P 0.5 - 5.5 mg/L, Nitrate as N 2.0 - 25 mg/L, and Nitrate/Nitrite-N 2.5 - 25 mg/L. Must be stored tightly capped at 2-8C. A NIST Traceable Certified Reference Material.