looking back a ways she seems stressed i noticed a lot of 3 & 4 fingered leaves, i try to wait to flower till they are at least pumping out solid 5 fingered leaves, im seeing a possible ph issue dont start adding stuff you'll make it worse! like jandre said flush with tap water you want that ca & mg in tap, check the ph, just run water for a bit maybe some weak mykos to keep the benies up, and just watch the new growth, slowly bring the nutes back in if all seems ok at 1/4 strength and just watch her it may be shes sensitive to nutes, that soil is hot stuff to start with,, do you have some superthrive? a couple drops in the water and a light mist will ease her stress, how are temps wild hot? cold? big swing from high to low?, check for light leaks, or something in there with an led on all the time, powerstrip light? cover with electrical tape if you find any thing. dont over react its not a big problem yet ,looks to be just old growth, it also looks like she might need N or something is preventing her from uptaking n, flush n wait is step 1
hope that helps