not sure whats wrong here

these are on 18/6, organa care nutrients( once a week), 400w MH, and they have started to look unhealthy, can any one give me some advice

looks like a case of over watering in the first one, heat stress in the sec, and nute burn in the last

Your leaves are cupping and burnt. Do some research for causes of this and see if something may make since to your circumstances. Have you sprayed the plants with an over dose of pesticides, is your room over heating, feeding to much, ect....