The reason why he stressed that is because the pellets have a tendency to stack and bond together.
I recently had a water softener installed and it's time to buy more salt.
The installer stressed, several times, I should use solar salt and not the pellets. The system saver pellets are just about the only salt available without looking at every salt vendor in my area.
Are system saver pellets an acceptable substitute for solar salt? ME, I would think so, but the installer was insistent.
Solar salt is the way it is made. The granules have to be large enough so they do not congeal into a solid mass, which is why you do not use rock salt.
Solar crystal salt looks like pieces of gravel in a driveway or along a road. It causes the fewest if any salt related problems in a water softener, and it is always the cheapest.
The one and only disadvantage, as with everything there is always disadvantages, is that solar will leave a dirty ring and sediment in the salt tank.
If you must, simply use a wet paper towel to wipe it out but with most softeners, not including the water powered Kinetico that usually will gag on any dirt so they require a prefilter with most of their models, that dirt will not harm regular softeners and actually can't harm any softener as long as the dirt is in the salt tank right?
The salt water is not going to get into your water and if it is sucked out of the tank, it will be sent to drain with the slow rinse water that provides the suction to suck heavy salt water up and out of the salt tank. And then (unlike Kinetico) 99% of softeners have a backwash and then final rinse after the brining cycle to make sure all the salt and any dirt is flushed to drain.
The down side of pelletized salt is the pellets get damp or wet and lose their shape becoming piles of grains of salt on the bottom of the salt tank and get rock hard. That's because they lay in a 100% brine and can't dissolve and that causes the water level in teh salt tank to rise into more pellets to cause more pellets to fall apart to the bottom of the tank and repeat the problem.
And pelletized salt always costs the most unless you buy potassium chloride which is even more expensive (up to 4 times for the same size bag) because it will recrystallize out of solution and that reduces the salt dose lbs per regeneration and that reduces capacity of the softener which will cause hard water to get through the softener. And potassium chloride is always pelletized anyway. So you have two problems with potassium and, with high salt efficiency settings of the softener you can need to use up to 30% more of it than regular salt.
I would suspect that much of he salt is extracted by evaporation in one form or another. Direct physical mining of salt domes or other deposits (if not using dissolve and evaporate techniques) would be an obvious exception.
What would be the physical characteristics that differentiate the suitability for use based on processing techniques.
Those old salt tanks are good examples of those that someone should have cleaned out 5-10 years ago.