I need help quick three weeks in to flowering big probkem

I woke up this morning and this is what my plants looked like they are sagging like they are just dying i dont know what to do i need help please i dont want to lose them i have the lights 12/12 400w hps they are in five gallon buckets no soil bubbleponics

Need more info kal...whats the watering situation?

yes that could be a huge contributing factor

They are in five gallon buckets the waters ph is 6 and has nutes in it the roots just grow down in to it

parts per million? temperatures? nutrient brand? additives? temperature of the nutrient tank?