My girls are droopy after switch to 12/12 and 600W...

Hey there so the lights can definitely cause an irritation, but it may be that coupled with the many watering sessions that are keeping them down. Since you're growing in soil i dont think it's anything to worry about when your ph fluctuates between the 6-6.8 level, and many of the nutrients tend to be absorbs better at the higher end, like 6.3-6.5 Since you've done a flush on the 1 watch for change, and then possibly flush the others. But I would let the plants dry a bit and then continue watering with ph'd water at around 6.2 with your bloom and micro nutrients, they may even be hungry for a higher dose of the PK seeing as they're just going into flowering. I hope you can get some good help from everyone and things turn around shortly.✌️