That is not enough to go on. If you can't describe it better we will need pics. Most likely without knowing anything and going by that description you have nitrogen overdosing. Thee solution is to flush that by running water of a quantity not less than 5 times the size of the pot through that with all the run off going away.
It may be worse, something like dead and rotting roots. Probably not.
please post pics and a few details about the grow if you want help. We need to know medium, feed schedule, probably nute profile (many newbs use veg nutes in bloom and bloom nutes in veg), what the pH is of the water being used unless it is hydro. If it is hydro we need 3 days of res measurements and to off details.
But with some pics we likely can figure it out with much less info.
