light cycle 12/12 to determine sex

My plants are only about 3 1/2 weeks old but they're pretty big and I don't have that much space (especially height) and Im changing the light cycle to 12/12. I'm gonna yank out the males and go back to 18/6. Is this going to harm the ladies? I know the males usually show sex before the fems but I want to make sure this is ok. I just really need the space and want to max. yield. What'cha thank? Any and all help is very much appreciated!!!!!

that would freak your plants outs, why would you want to veg after u yank ur males? If u had a limit on height I'd flower as soon as I could

I forget where I read it but it said to determine sex, change light to 12/12, pick the males, and change back to 18/6. How else can I take clones and know for certain that the clones are females? Am I just going to have to take the clones, label them up from what plant they came from, and then when I'm ready to flower, throw out the ones that came from a male plant? Isn't there any other way? That would kinda suck but hey, what ever I gotta do ya know? Thanks for the help.

Pics are attached. A couple look a littel droopy but it's not because of water. I mist every couple of days and water every 1 1/2-2 days. They had to have needed fert (pics from this past Sat) cause that's what I gave them and they perked right up. Let me know ya know what y'all think. Thanks again.

those babes should be preflowering soon anyway, but yea unless you can start spottin some females now your gona have to clone them all and see how it goes, good luck brotha

How much do you think I'd harvest off each plant now? They're like 1-1 1/2 feet, busy. They're Big Bud too. The last harvest was pretty good. We were afraid to fert too much so we didn't use much in veg stage and I think that kept yield dow. The last plant was a bout 3-3/12 feet and yielded about 3-3 1/2 ounces. Since I haven't mastered the cloning techniquel, I think I'm going to move them to a bigger room, about 6x6 and height isn't and issue. I wall's are cynder block and I can't paint them so I need to buy some mylar or something. Even if I move them I think I'll have to get some fluoro's for addtional lighting. Don't think the 400w is enogh light for all of them in a 6x6 room. Soo much shading. Lot's of things to think about but if I don't f it up, I'll be a happy pot head.