The reason i said too much ferts or salt build up is because when a plant tends to get too much fertilizer the leaves, especially the top leaves, go real dark green, at first they go real shiny and it looks like they are doing nice and healthy, there like at max grow mode cause they got every fert they need and more. Eventually these high ferts overpower the plant and the top turns dull very dark green whilst bottom and top leaves show burn signs and leaf drop. I often see my plants look like yours but they are overferted. Try see if you can underfert the next plants you germinate to see where the happy medium with ferts is. Now not that this or yours is overferted but i do strongly notice leaf edge curling and twisting as well as those big ridges on older fan leaves, what can i say but probably the plant is trying its hardest to process as much water and ferts as possible and either transpiring too much or the stomata have already given up.Yer it dose look like heat stress and temps but overferting will do the same especially when the leaves go from shiny to dark green. New growth dose look nice but soon turns dark also.Took me little over two weeks from the time i flushed from overferting to get my plants back to being almost normal and new growth staying a fresh green not dark and ugly. Probably some nutrients have locked too, purple stalks etc etc but this is only a guess.Ghetto your plant is definatly trying to tell you somthing, i know little of rockwool or pH in it but if all is sweet then consider the ferts are slightly too strong or possibly over time it has caused slight salt buildup. I dint even think you could get salt buildup in rockwool but i know little about it. Please consider what i have said, i dont say its the cause or fix but merely a very good observation. Peace
