LOL. I get what your saying, but I guess you two still dont understand the basics of salt.
When you state "IMPURITIES", are you implying to other elements? if so, are those compounds such as salt is?
Example - GASOLINE:
Gasoline is refined from crude oil, and some contains lead and other unwanted ELEMENTS.
ADDITIVES such as "TECHRON", a detergent used to aid in cylinder deposit build up.
Gasoline is Gasoline, but additives can be used to to boost octane and improve efficiency.
I really dont think people take the time out to learn basic chemistry when they get into this hobby and that is why they tend to have a lot of problems that can easily be fixed by adding or removing basic elements from the Water Chemistry. Such as Phosphate removers, and other things hobbyist get swindled into buying because they lack the information to resolve these issues by simply boosting calcium to evaporate the phosphates.
RIDDLE ME THIS: If the phosphates came in the salt mix already as a COMPOUND, how is it a phosphate sponge can extract them?
Here is an easier one:
There is sand in a sand box and somebody dropped a bunch of dirt into the sand box. You are trying to get the purest sand out of the sand box. So you run the sand through water and some filter screens. SAND IS STILL SAND, it Doesn't mean the sand and dirt are a compound, and that is why you are still able to remove the DIRT (IMPURITY) from the sand base. End result is clean sand.
Watching youtube videos and not doing your own research is like people who read the Bible and do not research what they read. They go on faith, so they still think the world is 5000 years old and Dinosaurs which carbon date millions of years old, where put here to test their faith.