Pre flower emergency.

Hello everyone, I'm having a small crisis right now because there are pre flowers showing up on my pants started from seedling and Im not sure which are male and female. One plant of eight has female pistils and almost all the rest have little nubs on the internodes suggesting male. is it possible that pistils come out after a few days from the nubs? or do the male nubs stay that way. can my plants get fertilized from pre flowers? they are all in veg stage with 24 hours of light.
Also the stems of some are turning purple. some of the leaves are turning up and some leaf tips are brown/dry. I think this is due to salt build up or over fertilization. two questions: 1.) how do i run a proper flush for a hydroponic system with rocwool, how many days or what? 2.)How much nutrients should I feed them? I started by giving them about 1000 ppm of sensi grow advanced nutrients because that is what their website recommended. lately tho i have been cutting the ppm down to 300 and flushing constantly (every three days for the past two weeks) and i have been feeding them pure water(ph perfect of course) for about two to three days at a time.
any help would be greatly appreciated. you are all a great help.

be patient the plants will show their sex when ready.

do you have any pics?

sorry max im not very computer saavy. but someday i hope to have the skills and a good enough camera to share with you all. maybe with the money i save from buying medical marijuana! But can the female buds possibly get fertilized from pre flowering or do they have to be in full flower before the male gives off pollen. I don't want them to have seeds.