First auto and coco grow

Small amounts of flowers starting still no smell at all. Not sure if anyone can help me but i'm getting some yellow leaves near the bottom and some brown spots on the bottom leaves. Also some purple stems. Started adding 1 tsp of epsom salts per gallon of water again to hopefully halt the purple stems. I need to leave town soon for 4 days and have been watering every day. Any ideas how I can water while i'm gone? Will it be ok without water for 4 days? It's in pure coco. Update today 12/25/17. It's grown a lot in the last few days. Now there is a very mild citrus smell. Looking good! 3 gal pots are too small for sure. Next grow is going to be in 5 gal fabric pots.