Blue Dream Auto

I don't think you really need a substrate EC pen, the benefit is in controlling the EC going into the medium "feeding solution" and minoring it coming out not checking when its in the medium, so many things will alter that reading from hot spots with different densities to amount of water saturated in its sample. and its best to water with some runoff when using hydro nutrients to prevent salt buildup as it will happen, no feeds perfect. I have seen PH probes for substrates and they can be useful, but more so for fields and larger grows. If your PH is off the bigger issue is fixing it, my last grow has something weird growing in the medium and its PH kept drifting down. I would water with PH 8, and runoff was 5.5 no matter how much PH up i used it would reset to 5.5 and lower, also used HP mix for that one. I do not like only peat, much bigger fan or coir and perlite. You can also make a slurry of the medium and use the other pens to find your mediums EC/PH if your curious. Any times your sticking things into the medium your damaging the roots. and some plants really don't like that, autos being one of them. Soil grows or things grown in earth are a different ball game. Good Luck!