TDS is one of those things that is only important when you have eliminated all the typical issues and still have a problem. Phosphates is another.

If you cannot bring your pool under control using our main-line methods (adjusting pH, and T/A then hammering with bleach to keep at the shock level for the CYA level) THEN and only then do you turn to alternatives. First you check for metals, and then and only then do you bother exploring TDS or phosphates as the cause of your problems. (Note: TDS and phosphates are totally different issues).

But pool stores, not being familiar with the PoolForum methods push stuff that requires unnecessary, extreme and usually EXPENSIVE measures without checking for the tried and true problems and solutions.

99.9% of the time TDS is bogus. 1 time in a 1000 it's valid to explore it as the cause of your problems.