Need advise please 4 weeks flowering

hi i,m 28 days into flowering afghan kush special ive noticed quite a lot of yellowing of leaves in the past 2 days with slighgt brown tips my ph is 6.2 growing in soil bio bizz all mix using biobloom thought it may be a mg issue so put some epsom in when i watered yesterday no improvement yet plz help no got camera back yet

We need pics mate that would help mucho

ive no access to camera till next week any advise appreciated how much yellowing is normal with 4 weeks left and with the brown tip is tht from over/underfeeding