Levelsensor device for saltcontainer of a water softener.

Every water softener like our "Seduction 16L Fleck" has a salt container, the salt is used for regeneration of the resincylinder. So, you need to check the level of the salt container on a regular basis and add salt if needed.. Easy to do: just open the lid of the container and look.
But why not improve the system a bit?

I made a salt level sensor for it: it has a RGB-led which gives 4 colors with the following meaning:

* green=level ok
* blue=level ok but add some salt in a few days.