how much yellowing

i am growing 2 plants under a 250w 6 weeks into flowering I have allways had a problem with yellowing and dying fan leaves and around week 4 of flowering i have given them a dose of epsom salts and am using biobizz grow, bloom and topmax nutes at recommmended dose ph'ing my water to 6.5 how much uellowing is normall it always seems to happen yet i see peoples pics of lush green plants was hoping to get some hash out of my plants but there are never any leaves left at the end of flowering

It varies from strain to strain. It is the natural cycle of the plant in the flowering phase especially after week four of flowering. Your plants needs have changed utilizing high amounts of phosphorus and potassium and little to no amounts of nitrogen therefore the nitrogen deficiency causing leaves to turn yellow and fall off on its own.