You will need to know the conversion rate of your meter (whether it's 0.5, 0.7, etc.). If you know this and you know the PPM or EC, you can concert PPM->EC and vice versa.

Read the manual for your tester. It should tell you whether to use EC or TDS solution to calibrate your device. If it is EC as you suspect, you can calibrate it with an EC solution and still test your nutrients with a PPM readout.