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.