I am using the blue lab guardian it works great but not cheap either. the lights will flash every 30 days to remind you to calibrate the ph. The ec or tds can not be calibrated I wasn't crazy about that I have been checking it with blue labs calibration solution and its spot on. i have used a blue lab ph pen in the past it was very good at keeping its calibration blue lab are good IMHO. I have used hanna pens for many years they are also quality meters. I have used Apera ph and tds pens they are goo d aswell. those are the three brands i would consider I dont go for the cheap amazon pens your asking for trouble.
Plant are looking great Stltoed