In the area I live the water is hard enough to make clothes stiff after some washing cycles.
I would like not to use two or three times the detergent normally required just to soften water. According to my experience, Calgon has no effect softening the clothes. Washing soda is good only for white clothes and I'm not yet convinced about the results of washing nuts.
I looked around on Amazon, mainly polyphosphate devices, but most of them are of poor quality in terms of production (they leak or after some time just split in two).
Do you know any kind of device, be it refillable or permanent, which I can apply before the washing machine? The treated water, of course, not need to be drinkable.