I can understand when someone is trying to trouble shoot a problem they can't put their finger on , but post like this are a waste of forum space...the anwers are all over the internet ...you would of got an answer quicker than making this post.
I'd clone that bitch ready for the next run:-o
I'm sure you have already but go into the tent when lights go out and make sure it's 100% light proof, check zips n all.....to make sure they flower right.
It has to be as you can see it's fried out, specially the new growth on top...makes it very obvious & I've seen this before with my own plants once apon a time.....
The lime has probably stopped buffering your PH , so...its not acidic enough to have all availability nutrients for the plant. some will add more lime or PH TO 5.8 instead.
It just got abit low on nitrogen, or they would be more darker, thou I'd just let it be...i wouldn't be adding that at this stage of development unless you want more potential issues.
They'll improve with 12/12, they love the light at this stage and it aint too late, I've bumped up my lights an extra 600w on week 2 and was an impressive yield.
Just calibrate it with the solution you have , if thats the only option..get it to the best range you can...and if you know the ph of your tap water that is a bonus to know if you are a point off is no big deal really till you have something more reliable.