I’ve got a hm 80 ph pen mate they great for a month or 2 but then need constant recalibration I’m pretty sure it may have dried out between grows though I’d go the blue lab mate I think by memory they are an extra 30-40 bucks n come with storage solution calibration liquid n such never let me down yet just clean the probes back in storage solution and she sweetI'm getting a hm 80 for the ph pen I had 2 before and thsy where pretty good