Hydrion Quat Test Paper QT-10, 0–400 ppm

Quaternary ammonium — quat — is the other common food-service sanitiser, and it cannot be checked with chlorine paper. Different chemistry, different indicator. The QT-10 paper reads quat concentration from 0 to 400 ppm against its own colour chart.

Getting quat concentration right matters more than it does with chlorine, because quat has no smell to warn you when a bucket has gone weak. A dispenser that has drifted, a bucket topped up with water through a shift, or a concentrate diluted by eye all produce a solution that looks and smells exactly like a working one. The paper is the only thing that tells the difference.

The 0–400 ppm range brackets the usual working concentrations, so the same paper covers both a 200 ppm sink solution and the higher concentrations used on equipment surfaces.

Two things affect the reading and are worth knowing: hard water raises the apparent requirement, so a bucket mixed to label strength in hard water can still test low; and quat is absorbed by cotton and some cloths, so a bucket that reads correctly when mixed can be well below range after an hour of wiping. Test the bucket in use, not the bucket as mixed.