Not many alternatives
I have a handheld TDS meter that I use to monitor the water quality of my reverse-osmosis unit. It is supposed to be calibrated with 443 ppm (not the 800 ppm of this pack) and can't handle anything over 999 ppm. Traditional calibration fluid for hydroponic meters is way above 1,000 so it can't be used. There simply aren't a lot of options out there. The good side is that it is easy to tear off the top of the packet and stick your meter inside, and you can be confident it hasn't evaporated in storage. The bad side is that it is still too high for ideal calibration. I'm still uncertain how accurate my two meters are. Despite being sold as factory calibrated they read quite differently - one significantly too high and the other too low. I guess I'll have to go to a medical supply store to see if I can get normal saline there and use that to calibrate my meters.
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