Sizzilky, looking good but would recommend some fertilizer/nut's at least up to the last 3 weeks if not 2, then flush for the final 2 weeks, fish extact fert works well (This would also explain the yellowing in the lower leaves). They should also be a lot bushier for a 600watt grow with HPS... you mentioned you only have 2 weeks of flower left so better luck next time, but definitely an ok grow. Cheers