6 weeks into flower!! yellowing leaves

so ya im six weeks into flower. the leaves are starting to yellow. DWC...im using gh three part. right now im using a 0/2.4/4.8 ml/1.5gal solution and 9ml awesome blossom/1.5 gal. everything has been going fine until the past couple weeks. the yellowing is getting worse. im planning on just using ph'd water for the next three weeks before harvest. ph 6.0-6.3 not sure what it is. any help is appreciated. my grow log thread is in my signature. take a look at my plants. thanks

room temp. 76-88

They look a little tip-burned, but for the rest, yellowing late in flower is common. If you haven't drained and refilled your res recently, it would be a good time to do that.