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I place some water in the "cup" at the top and push a button and hold.HTM
The strips seem to work OK but I find the range isn't very good. I think there's a marker on the strip for 1500 and the next one is for 3000. If you are looking to make sure it's under 2000 it's hard to judge with the way the strips are setup.
I would not recommend using a spa with TDS over 1500. 3000 is useless as well as the pool should be drained at 2500.HTM