Hach TNTplus 840 nitrite test, high range (HR) 0.6-6.0 mg/L NO₂-N (nitrite as nitrogen). TNTplus vial test for lab or field use with Hach DR3900 / DR6000 / DR1900 spectrophotometer or DR300 pocket colorimeter. Wastewater treatment plant effluent monitoring, aquaculture water quality, cooling-tower biocide verification. Barcode-vial format eliminates transcription errors. Ships pack of 25 tests.