Just make sure you know what the three calibration points are for your PH pen and you can use any solutions. However, with the DS meter i believe you have to use there calibration solution due to the calibration set point. Personally i felt that the blue lab pens where over priced. If maintained properly you can use vivosun pens and get just as accurate results. Less than 20 bucks on amazon for both PH and DS pens.