Older leaves curling and dying every day

Defo looks like heat stress with not enough air flow

I believe it is a lack of run off and fertilizer build up in soil causing ph issues. Which causes toxicity and deficiency signs at sane time like I am seeing. Only you know if your getting a good 20 percent run off of what you put in.

In picture 3 there is a leaf that has spots.Look under leafs really well with magnifier. It might be a pest,mixed with a toxicity or def. Like grandma said keeping a diary will start to help it's crazy. Hope to see more grows my fellow grower.blessings on all u grow.

Heat is not the problem, to me it looks like too much fertilizing, an easy problem to solve. Remember in soil it is a schedule of plain water/plain water/feed/plain water/plain water/feed.......... so that the plants are being fed every 10-14 days, which is plenty in soil based cultivation.

Is this an autoflower, @Ginseki? If so, the soil might be just too hot for them (i.e., giving them too much "food"). I would also say that adhering to a fixed schedule (every 3 days they get 1.5L...) is not the best way to grow these babies! You need to "read" them and give them what they need when they need it. This is especially true when doing an outdoor grow - temperatures/humidity/cloud cover etc will all affect the plant's need for more (or less) water... For example, just this week we had two very hot, dry days... 4 of my ladies needed water TWICE a day! When the temps dropped (thanks to some cloud cover), they didn't need that much. So, how do you know they need water? Lift up the pot and see how light it is... if it's super light, they need water! (My current grows are in 3 gallon pots and the ladies I have that are the same age are now averaging 1 gallon a day... and soon will be requiring more). Your PH sounds perfect... I just think they probably need more water! Good luck!

I will expand the info, since i don't have a diary, the plants germinated April 14th, now they are in 30L pots and i water them every 3 days with 1.5 liters, checking the ph every day (callibrating the device every 2 waterings) aiming at 6.4-6.6, i'm using hydrobuilder supersoil recipe + biobizz (using the schedule for rich soil), this month i have 14-13 hours of sun.

Without a diary, we're flying blind here.... It's most likely nute burn - and most likely you're giving it too much nitrogen... but I can't tell you how to correct that because I don't know what it is you're doing. It might be a PH issue - but we don't know what PH you're maintaining... it might be over- or underwatering (either one causes leaves to curl down but then so does a nitrogen toxicity).... OR it might be nothing since older leaves do start to dry up and fall off at a certain point in the grow ... but we don't know even how old the plant is without a diary! In some of the pictures, I'm seeing evidence of a calcium deficiency.. this could be caused by an excess of nitrogen as well - but can also be caused by an improper PH level... Oh dear. PLEASE start a diary - even if it's to cover the last week or two weeks... it would help us help you! Good luck