yellow leafs..

Got 2 autos,,,,,UK Cheese and sperms skumk. The cheese has yellowing leafs on the bottom and it's starring to bud the Super Skunk none of this. The both grow in roots organic emerald mountain which is organic and stays hot for like 4 weeks the cheese is a slow developing purple stems???

pics of the purple ? a lot of strains naturally have purple stems on the leaves...... the yellowing could be from lack of light ..... if the top is dark green then its light if the whole or most of the plant looks lime/yellow then its a N def