TDS much lower than expected

[wa2asb]

I've been using bleach off and on for the last 6 years (can't use it when I'm out of the country). I remember a "know-it-all" at a pool store telling me the problem with it is that it raises the Total Dissolved Solids (TDS) more than using the "tablets". Of course he didn't mention that using the tablets raises the CYA.

I was also using lithium, but it has been very hard to come by as of late, not sure why. I know lithium is expensive, but compared to the price of the pool and of running the pumps (2.5hp pool, and 1hp for the streams, not to mention the fractional motors for the pond and two fountains).

So I got to thinking about TDS and bought a meter to measure it. The results were rather shocking: the pool water read 157, but my tap water was 260. The filtered water (LG filter) in the refrig gave me 148. Ozarka bottled water was 13.

Two years ago the CYA was 100 and I replaced about half of the 35,000 gals in the pool, and the water surface is 1,059, which is high compared to the gallons of water because the pool is shallow, but it means a lot of evaporation and fill water from the tap.

So I'm really puzzled as to why the TDS in the pool is reading so low. My CYA is 60 so I'm running 5ppm of CL, and I'm wondering if the high CL could possibly be giving me a low reading? Anyone have any ideas?

[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.