I used to have a tds meter just like yours. Someone mentioned the inaccuracy of the tds meters on this forum. I asked which meter to buy and the Hanna PWT was the recommended one. I bought it from a Hanna dealer on ebay for $60. Buy calibration fluid at the same time.
After receiving and calibrating the meter, I tested some cs that had been hanging around ... about 6 months old. It was deep yellow and yucky looking. Keep in mind that I had always made my silver 18 ppm. This old cs tested at 26.
Yep, investing in a good meter is well worth the price !