TDS much lower than expected

[waterbear]

Which TDS meter do you have and do you have the standard solution to calibrate it against? If so when is the last time you calibrated it?

[wa2asb]

It is a HM TDS-4. It is brand new - this is the first time that I've used it.

I suspected the meter might be off, but it gives consistent reading +/- 4 on the tap water and on the pool water.

Say if it was off by a factor of 10 and the pool was 1570 and the tap water was 2600, that still doesn't account for the pool being less than the fill water.