I think TDS is kind of overrated. Ya know I am going on 10 months with the same water, less adding water to the spa with fresh. I use Defender once a week, I hit it with Leisure time Replenish once or twice a week depending on use. I watch the PH/ALK and change the Nature stick every 4+ months. I understand all the crap that goes with it. But we use the spa a few times a week this time of year and the kids are jumping from the pool to the spa more times in the summer because my pool is not heated.
The Key is be proactive about your chems, don't sweat the small stuff the dealer tells you or the mnfg tells you in a book and enjoy the spa. It's not going to void your warranty so why worry. Not saying a water change is bad or un-needed, but if the chems are taken care of you should be fine for quite awhile.
