New grower again, 8wk flower, GSC, in soil 707, ph checked always, ppm 500 to 600 out is still high, I think, 1200 to 1500ppm, but fan leaves yellow then die, any ideas? Thanks

Hello all. I'm a first time grower. 1st week of flower. GSC in Formula 707, Connoisseur Bloom with bud igniter and sensei cal/mag. It looks worst in photo. Only see it on a few top leaves. Thank you