Ok where do you takie the temp in your grow area?
Probe/sensor is at level of the plant crown, i.e. top
Light schedule?
24/0
Do you ph you water when you feed it to your plant. And if so to what ph. You in soil right? If so lets just focus on phing what goes in and not to much on what comes out.
in soil, a good loam cut with 1/4 perlite, ph'd in an out, both close to 6.4
I am sure you have a deficiency. The issue is it from it needing more nutes or a ph issue. Ph will lockout nutes and the act of adding more nutes to a lockouted plant will casue even more problems and lead to dead plants.
You nutes are 6-9-0? if so that there is another issue. For veg thye are out of whack. You wnat a higher N and pretty close p and k. instead of 6 n 9 p and 0 k.
Not precisely 6-9-0, i top dressed with 1 tbsp of 6-9-0 bonemeal, mostly been depending on the alfalfa tea, about 1 week ago was using manure tea but didn't seem to help, teas also have molasses at 1 tsp per gallon
When they are dry I would flsuh with plain phed water. This will reset the medium to the phed level. Than the next time they need watering after wards I would feed them 1/4th strength veg nutes. The ones you will go get with a higher N than P and K. Make sure you ph the water after you add the nutes. Nutes can drop ph big time. Than if the like the nutes increase the strength slowly. Feed once a week.
that's where i was heading, everything was looking good, and then fell off a cliff
Regardless of your issues, once we make sure evrything else is fine this watering and feeding should fix the issue. I perosnally think its a lack of some nutes compouned by lockout from ph of others.
it's not ph, i've checked that close, and i do trust the drops, not so much meters unless they are the high end type
It will take some time but we can save them and they will recover
good advice, what i needed to hear +rep