Multiple sensors, all reading +/- 4-5%, which is normal. I tested with digital one, bme280, ac infinity. I'll test using the water+salt method and see the numbers.
Hydro setup, water temp at 68° steady. I also tried to play with water temp, it gives a huge difference on leaf temp!
I love this shit, so many things to see/test/change!
I appreciate you response and I need to apologize for the tone of my postings. No excuse.
Re. RH 4± - I switched from a Pulse + Inkbirds to AC Infinity and their humidifier. I calibrated using salt but you can also get a Boveda "kit" which consists of one packet and instructions. The Boveda is quicker and reusable.
Water temp changing leaf temp? I could see that being an impact of having a big bucket of water ameliorating temps but, other than that, the two main factors that would drive LST would be ambient temp, IR radiation (very little from LED's), RH, and wind speed. My grow is in a 2' x 4' tent and the res holds 28 gallons so I know if buffers temps for me. In your setup, would you res have enough thermal mass to impact your plants in that way?
Re. VPD being an issue - what I wrote was describing the problem the wrong way. VPD = a combination of RH, and ambient and leaf surface temperatures. I assume that wind speed is assumed to be 0. Given that VPD is just a proxy for, primarily, ambient temp and RH, if your grow isn't doing well in what is considered an optimal range of VPD values, that has nothing to do with VPD. What it means is that your grow isn't growing in what are considered optimal ranges of temp and RH. That's key — VPD is just a way of expressing two numbers (temp and RH) as one number.
If we take the idea of VPD away, the issue is that your grow is not thriving under RH and temp where cannabis is known to thrive. One question to be asked it "Why?" but another, arguably valid question is, "Who cares?". I'm not being facetious, lemme explain.
Metrics are key to reproducibility, with an underlying assumption that reproducibility is, actually, a goal. Unless you're a stickler for detail, as I am, does it matter that this grow/strain isn't growing under what we humans describe as optimal conditions? The plant's happy and, unless you've got to go to extraordinary lengths to keep the plant healthy, then maybe is just the way this grow/strain functions. I'm not advocating "Lie back and think of England.", if you're familiar with that phrase, but, unless there's a need to "fix" this issue, perhaps it's OK to roll with it.
The "If it ain't broke don't fix it." rule be well applied here. Shift the focus from being on VPD to "is the plant healthy". That grates me, personally, because I'm a process-oriented person (software engineer) but, unless this becomes an ongoing issue, how would "Just let it ride." work for you?