So.
I've been reading various threads on sensing of the level, that is, remaining salt, in Water Softener systems.
Examples are: @aaron's [PROJECT] Salt Tank monitor using Arduino & MQTT
And: @ireallyhopethisworks Height of a loose solid material - #9 by ireallyhopethisworks
And: @rlithgow1's idea here: What Have You Added to Your Setup Recently? - #63 by rlithgow1
All of these are great, and are quite different from each other, but when I thought about them, I realized that what I was really looking for, wasn't the level of the salt, but a notification that I need to buy salt. Any value between "full" and "buy salt" is irrelevant.
So, after much thought and consideration of the time between "need salt", and the execution of a purchase of the salt, I realized I needed an alert at about 50%.
I also wanted to keep it simple. More along the lines of Rick's water sensor than the other solutions.
Thinking on this eventually brought me to my solution.
Here are my components:
Plastic Hinge: McMaster-Carr
3M VHB: Amazon.com : B09PD969P9
Zooz ZSE43 tilt and shock sensor: ZOOZ ZSE43 TILT | SHOCK XS SENSOR – ZOOZ
Zooz weatherproof case: Waterproof Case for the Zooz XS Open | Close Sensor - The Smartest House
And a yardstick. Although, any similar piece of wood, plastic or even a PVC tube would do.
I used the 3M tape to secure the hinge to the lid of the salt tank, and then the yard stick was secured to the hinge.
The yardstick was cut down to 17" in length, and the sensor in its case was attached to the end of the remaining 17"-Stick.
Basically I put the sensor at the end of a hinged arm.
When the tank is >1/2 full of salt, the arm rests on the salt, and the tilt sensor is "open". When the tank is <1/2 full, the tilt senor is "closed" because the arm is hanging free (vertical).
The trigger for an alert is when the sensor becomes closed.
Everything except the hinge pin and the screws for the case are effectively corrosion resistant.
Simple tests seem to indicate it works. However I just filled the salt tank...
I tried a Ecolink TiltZwave5.0 and it wasnt sensitive enough. It require a jolt to get it to report closed in the vertical position. The Zooz Xs ZSE43 seems to work better and is much smaller. We'll see what its battery life is like.
Photos aren't great, but they are below anyway.