ufff,great sativa,man! beautiful looking colas. My Golden Tiger's big fan leaves have started to fade faster as I'm coming close to harvest.Landrace sativa hybrid,just like yours.Plant is drinking,pulling nutes from its leaves,firstly from the lower part where the light is not strong enough.Not a problem at all.I wouldn't increase Nitrogen as there is no need to.Focus on the buds,this natural yellowing won't hurt your yield or bud quality.