The most common hanna ppm testing solution I can find is 1382. With this chart you can calibrate pretty close. I think you should email hanna with the meter number and get a definite answer. I've lost crops because of wacked out meters. Might not be a bad idea to back up whatever you decide to do with some drops or strips. I'm sure you know all this but that's all I got
http://www.gardenscure.com/420/hydro...ion-chart.html