HELP!! Is this overheating/overwatering or other issue?

you cant water daily such big plants, they need around 3-4 liters each every 3-4 days i would say, if you water little daily, part of root zone never gets humidity, that could lead as overwatering to pH imbalances i see empty bottle one the ground, one girl watered, rest dry. you have bad habbit there annd it could be the answer to your problems, even if the rest would be done by book.

Hey @GrowingGrannie. The amount of water per day is not updated, my bad :/ We are using at least the double in this stage (about 600-700ml) I don't think is underwatering, since it's taking more time for this plant to absorb all the water (in comparison to the other days and to the other plants which are healthy). The pH probably is not the issue. Because we are using pH controller with the nutrients since the beginning. Also, as I told the others look fine. I think this plant suffered from heat stress. But besides that, another problem is affecting her. My guess is overwatering, so we used only pH-balanced bottle water and cut to half the volume used. Thanks for the support guys! If anyone has an idea about what could possibly be the issue, please tell me!!

She needs water, bad. Between heat stress and under-watering, she's looking rough. Just make sure to keep the soil moist, but don't overwater. Plants need oxygen as well as nutrients and wet soil doesn't let that happen. I hope this helps. Good luck!

I think this is a result of two problems - the proximity to the lights you mentioned (the temperature in the tent is fine!) - that accounts, I think, for the discoloration you're seeing on the upper leaves.... but the biggest problem is most likely underwatering... You're only giving .09 gallons in a 24 hour period - plants in flower are going to require a lot more than that! When you water (as opposed to feed), make sure you're getting about 10-20% runoff... for her, I would get that runoff and then let her sit in it for maybe 30 minutes to see if the pot doesn't soak some (all?) of it back up into itself... and then pour the remaining water away since you don't want her to have wet feet... Good luck!

She looks like not watered at first, but damaged mostly top with rusty spot and clawing leaves - 99 % too low ph was given. I had it only after applying sugars to soil. I see other girls are ok in the background so if you water same time same thing its too big difference for my guess, but its only thing i could thought off seeing this

ph is way out of range, that will bring nutrition issues too either transplant into 2x pot or flush i grow weed 7 years and ONCE only made flush right, always was overdrawning stunt plants, i think it a myth, same as you cant transplant in flower. make sure your ph is in range and no cats pissing into pot ;) so either water 2x amount of pot size through pot , but only DE-chlorinated RIGHT/CORRECT pH water to be used - aka flush keep pot above something for better drainage, don't rush and let it runoff all amount and LET HER drink - pot should be light before you give her any water again !!! spray with 0.5-1ml/l calmag added, 100 ml spray daily for that girl will be more than enough. use only that day mix for spray and that should be her only food for next two watering after flush or just drop it into 2x bigger pot with fresh soil and FOLLOW GOOD pH ! Happy Growing !!!