Relative Humidity and Saturated Salt Solutions

After sitting for a week, the solutions will be saturated and in equilibrium with their solid salt precipitates in the same vessel. As the salts are different, their saturation points will be different.

Changing the relative humidity and the speed of the passing air, assuming the vessels are open to air, will cause evaporation or condensation, altering the amount of water in each vessel, and causing each vessel's contents to approach equilibrium.

Without more context, the probe fails to have any meaning at present, as do the words "high" and "low".

Altitude affects pressure. Pressure affects water's boiling temperature. Heat of solution will be different for each salt.

I think that you are missing the point.

The question (though it is not well expressed) is about calibrating an RH probe with saturated solutions in equilbrium with the air above them. That air is then at known and published RH levels. The vessel must of course be sealed.

I agree that 'high' and ' low' have no meaning.

What kind of probe you use?

Is it a hygrometer, to be calibrated in RH?

For what range you want to use it?

Is it an open type, mechanical or electronic?

With probes you should make sure that first the elements are contamination free,

You can then saturate them with clean mineral free water - this will be your 100% if you do it at the right temperature.

Then your probe will dry out and you can continue as the Australian poster explains. If you want to make sure all is ok get also samples of the air in the bottles and run these through a wet and dry thermometer hygrometer type (best with suction) and read the moisture on the table. Once you will calibrate probes in the ppm or ppb range, you'll need a different setup. Good luck.