Does anyone here know what causes leaves to curl upward???

Been looking through the sick plant threads all day and cant find exactly what im looking for lol my plant is 2 weeks into flower under my 400 hps i left for 3 days and forgot to raise the light but when i got back the top bud was toast its like a tan color on top and hard its only the top and the rest of the cola is growing still but the leaves are curled upward at the edges but only the top ones im wondering is there a cure to fix this ? i moved the light my ph is good using lucas formula and big bud from AN some people say the leaves curling up is a nute thing but its only like 5 of em on the top the rest is 100 healthy in my waterfarm sooo any clues thanks

too hot/too much light, back the light off and get the temp down

capncash said:

too hot/too much light, back the light off and get the temp down

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I SECOND THAT. DAMAGE IS IRREVERSIBLE WHEN ITS BROWN.. YELLOW IS FIXABLE BROWN IS DEAD, GL BRUDDA THEY SOUND GOOD

https://www.rollitup.org/marijuana-plant-problems/352122-help-one-dead-very-quickly.html

its almost 100 up hurr in seattle hahaha so temp down is not as easy as it sounds haha but i did back my light off and im also thinking that on the off chance its a mag deficient im adding a lil epsom to the rez and ill folliar with epsom tonight at lights out does this sound right? stop me if im bout to make a mistake with the epsom haha