What is the problem here?

Creepy_Steve is spot on....

paling from bottom-up on plant and tip-in on leaves? Nitrogen deficiency.. a suggestion -- get over the "everything is fine" when something is going wrong feelings... because clearly something is off. LOL. It's going to get in you way of properly deducing what is wrong if you never think what you do is wrong. reatios and concentration are important. you may be spot on with some pre-ordained targetted concentration, but if not in proper ratio it's still going to cause problems. In soil this is a matter of trial and error and depends on variables that can be wildly different from one garden to the next depending on soil and products used in the soil. Soilless is more precise in figuring this stuff out. if you do soilless, simply make use of a ppm calculator and start tracking upper/lower thrsholds when you see symptoms occor and avoid those thresholds in future .. or in the case of upper boundaries.. push them as best you can. you can do the same with soil over time, but it will take a bit more effort considering all the moving variables used. it's good that you are staying on top of pH ... that makes diagnosing much simpler. Make sure description at beginning of this message matches progression of the symptoms, if so, it's pretty clear-cut nitro deficiency.. . do small bumps up because it's not a huge problem and most of what i see will heal itself unless you start seeing dead spots. yellowing will reverse. 5-10% bump to component with most N while not drasticalyl changing other things is best option. It's always good to have N isolated a bit among your fertilizers... some component you can affect withotu changing other things much is very useful, as N seems to be the thing most often adjusted, ime.

Hey mate I think I know what's going on here. Are you, by any chance, watering them with cold or cool water? I try to fertigate at the same temp as the substrate which is sort of luke warm - I have noticed whenever the water is a bit cooler, the plants all droop for an hour or two as if they had been sleeping.

Hello, i have an Idea, do you know AI chatGPT? I just asked him a question, sent a link to the journal and got answers :D

i agree about possible nite deff.. i would feed them some, not sure what nutes you have on hand or if your man or auto water.. but i would try that and keep an eye on ppm. mine cleared up after a flush.

Slight yellowing indicates possible lack of nitrogen. Maybe give them a little boost of the grow nutes on the next one and see how that fares. Won't repair the yellow done but should stop the spread.