RavenNS,
Since spas are drained and refilled every 1 to 3 months TDS is not an issue if they are properly maintained. The problem startes when people start dumping unnecessary defoamers, clairifies, fragrences, etc. into the water. Also, many people, including dealers, just don't understand bromine chemisty. Look at the number of people who just put bromine tabs in a floater and don't put sodum bromide in the water with each refill for an example and then wonder why they can't maintain a sanitizer level.....or the number of people who don't realize that chlorine is probably the most effective way to shock a bromine spa (or that almost all bromine tablets contain chlorine also for this reason!)