Polyphosphate: frequently asked questions


What is polyphosphate treatment used for?

Treatment with polyphosphate is a simple and effective solution to limescale problems. When dissolved in water, polyphosphate prevents the formation of limescale, by preventing calcium and magnesium from bonding and crystallising. The polyphosphate treatment does not reduce the total hardness of water and, when used for a long time, it creates a thin protective film on surfaces, preventing corrosion and dissolving any existing deposits. Polyphosphate may be used, for example, to protect the boiler and to protect specific household appliances, such as the washing machine.


Why does water appear milky, whitish after installing a filter with polyphosphate crystals?

The problem might be related to the period of use: as a general rule, polyphosphate filters must be used continuously. If for any reason, water does not go through the filter for some time – longer than a week – the crystals must be replaced.


Why do the polyphosphate crystals in the filter look ‘dissolved’?

This might depend on the contact with hot or warm water. In contact with water, polyphosphates start being depleted: higher temperatures increase the speed of this dissolution, that is why it is essential never to expose polyphosphate to more than 35°C. Although the polyphosphate filter is protected by a check valve that prevents any hot water backflow (as specified in the instructions), sometimes, after prolonged inactivity, especially at certain latitudes and/or in the warm season, the ‘standing’ water inside the pipes might warm up to the point of causing the phenomenon observed when the water flow resumes.

Why is the polyphosphate charge of Dosaplus not being depleted?

If the charge is not being depleted, the suction nozzle in the filter head might be clogged. To clean it, unscrew the nozzle, extract it with small pliers and clean the hole with a thin needle, having a diameter of 0.2 mm.


How often must I replace the polyphosphate?

Polyphosphate crystals must be replaced at least every 6 months, even if not completely depleted. At any rate, you must refer to the instructions and follow them.

As a general rule, however, the polyphosphate must be replaced when it looks different from when you charged it.


What is the difference between polyphosphate filter and softener?

Polyphosphate dispensing cannot be viewed as an equivalent treatment to softening: the resins contained in a softener remove calcium and magnesium from the water by carrying out an actual softening process, in which total hardness is actually reduced. Polyphosphate, on the other hand, inhibits the scaling action of calcium and magnesium carbonates, so that they are discharged without forming deposits, therefore it does not reduce the total water hardness.

Treatment with polyphosphates is not recommended at high levels of hardness: if the water taken in is very hard (35°f - 350 ppm of CaCO3 or more), the treatment becomes progressively ineffective and some limescale deposits appear. That is not the case with softening, which is effective at all levels of hardness.

In household applications, softeners are generally set up to reduce hardness to around 10-15°f. Due to this residual hardness, the polyphosphate dispenser is a good additional solution if placed at the boiler inlet, to prevent any limescale from precipitating due to heating the water.