really could use a pic.. do you have a camera on your phone?? it's just too hard to correctly diagnose a problem without a picture. Plus, there's a lot more info that you left out for any of us here to help you out..
So are you soil or hydro?
what type of nutes are you using?
what is your ppm?
pH?
growing medium?
what type of lights do you use?
That's usually enough general info to get some good help. and like I said, a pic always helps.
Now, I know someone posted that you have nute burn....But I am not sure how he can be certain that is your problem without more information. I would advise you to NOT flush your plants yet. I'm not saying the person is wrong, it could be nute burn. I'm saying a little more info first so that we can be sure... Please answer the list of questions and let's see if we can figure out the problem...