I’m gonna buy the HM tds meter and see what readings that gives me for tds.
When you buy a new TDS meter, also buy some calibration solution at the same time. The meters say they are factory calibrated, but I've recently bought new meters (like you, to replace cheap ones that I didn't have confidence with!) and they were actually quite off.
Get a calibration solution that is close (maybe just above) the value that you are going to be measuring. 342 ppm is common.
When choosing a new meter, get one that is temperature compensated for more accuracy. I've recently bought the new HM Digital AP-1 which seems pretty good and is not expensive (even with shipping Amazon US to Singapore). Easy to calibrate and seems consistent with readings.
One other thing I recently learned / realised that I think is useful to understand: there is no such things as a meter that measures TDS. There are only meters that measure conductivity (EC) which have been programmed to multiply the measurement by a given factor to give a "TDS" readout. The factor used varies between manufacturers and depending upon how you calibrate the meter, and possibly also across the measurement range depending upon how the meter is programmed. You can calibrate the meter for either NaCl (most common, for aquariums) or 442 (more for hydroponics) - both have different factors that EC measurements are multiplied by, and hence give very different ppm readings.
For example, 700uS/cm conductivity could read 341 ppm TDS (if meter is calibrated with NaCl) or 481 ppm TDS (if calibrated with 442 solution). Almost makes you think that discussions of TDS are pretty meaningless given how much variation there could be if we were all to measure the same water with each of our meters!!!
Really it would be much better if we all swapped to EC meters and talked about conductivity, then we'd get rid of all this calibration / conversion uncertainty. But TDS and ppm is in our heads, so I guess we'll all continue to discuss and chase very precise TDS numbers that in reality have a massive amount of uncertainty.
TDS readings are really only any use in monitoring your own water conditions from one day to the next and getting a feel for how they are changing. If we want to compare measurements with each other, we really all need to switch to conductivity (EC), not TDS.
Apologies if the above is obvious to others, but it wasn't to me and I couldn't understand why my TDS readings were so different.