I have the strips, they are worthless, kind of like a speedometer that goes from 0 to 90 to 250mph with no graduations in between.
Having owned my tub for 18 months now I have a good sense of when the water needs replaced, and that probably is when the TDS is high.
I'm in a good point in my water care regiment, I changed my water in early July and I looked at it last night and it still looks real good. (alk 110, PH 7.2) I'll be shooting for Oct before I change again. I just mention that because that seems to be almost every newbie's concern, can I get this water thing down? The answer for everybody seems to be yes. The advice here helps a lot, but there is a lot to be said for learning by your mistakes.
Getting back to TSD measurement, I understand what it is, why it is important, but I don't measure it. If you have only had your tub 2-3 months and things look good, go ahead and change your water just to get a reminder of what new water looks like. That done, I think you develop a good sense for when its time to change.
