Product Dose from Active Strength

Almost nothing in a drum is neat. A "50% caustic" is half water, a nitrite closed-loop product may be 20% sodium nitrite, and a scale inhibitor blend might carry 8% active phosphonate with the rest as azole, polymer, dye and water. If the specification says you need 100 ppm of active nitrite and the product is 25% active, you must feed 100 × 100/25 = 400 ppm of product. Miss that and you are running at a quarter of the protection you think you have.

The trap runs in both directions and shows up on test kits. Most field kits report the active (a nitrite kit reads ppm NO₂, a molybdate kit reads ppm MoO₄) while your feed log records product. When the two do not line up, people chase phantom leaks or overfeed. The fix is a single line at the top of the log: "target 800 ppm product = 200 ppm active nitrite." Note too that suppliers reformulate; when a drum quietly changes from 25% to 20% active, the same feed setting silently drops your residual 20%, and only the label tells you.