When a washed surface leaves a whitish mark on drying, the first thought is inadequate rinsing, but the cause is often the minerals in the water. Hardness comes from calcium and magnesium compounds; when the water evaporates these salts stay on the surface and form a white film.
| Hardness (mg/L CaCO3) | Class |
|---|---|
| 0-60 | Soft |
| 61-120 | Moderately hard |
| 121-180 | Hard |
| Above 180 | Very hard |
Mains water hardness varies from region to region and most businesses do not know their own figure; a test kit or a laboratory measurement says which measure is needed. If the value is low there is no scale problem and the marks come from something else.
- Measure the hardness of the rinse water once.
- Where possible, make the final rinse with softened water.
- Speed up drying: a droplet standing on the surface leaves a mark as it evaporates, and wiping the water away or blowing it off is cheaper than a chemical answer.
- For scale that has built up, choose a cleaner that suits the equipment.
Scale dissolves in acid, but a galvanised coating is stable in the pH 6-12 range; outside it zinc corrodes faster than normal (Galvanizers Association of Australia). On a container with galvanised parts, as in the Isotec TBX models with a galvanised steel pallet base, do not use an acidic product for general cleaning. Abrasive scrubbing also consumes the protective zinc layer.
Water softening becomes an investment question when washing volumes are large and scale removal has become a routine maintenance job. In a business washing a few containers a day, drying discipline is usually enough.
