its either magnis def or natural genetics because mine was like that and its a indica strain . so flush your soil or res and use a nice batch of nutes and that should do it .
The purple stems arent that big of a deal, but the leaves drooping isnt a good deal. I can tell you that it is most likely over feeding. I had this exact problem It is a shitty situation because it is going to take a while for them to bounce back depending on how bad it has become. So what I would do is just keep giving them PH treated water and no food, or if they are hydro get the roots into fresh water and just make sure you have good air movement in the water. Last thing is (this is going to take about two weeks for them to bounce back) give them one good fouler feeding. I would put money on that fact that this will work. So good luck man.
haha if your in rock wool its definatly your ph. soil should be 7, one of my plants has turned completly purple stocked and the leaves are dying, o well it still looks good.