There's pH Up and Down available at your hydro shop/grow store. Also there are things people use to do the same things. Like lemon bring it down...there are different things to use that you probably have. Maybe somebody will come by this that knows?? I just have always used the ph up and down solutions as I am hydro and deal with it every day practicly........
MG soil is not the choice of most mj growers as it has time released nutes in it that will burn the piss out of your girls........unless you used to using it, I guess, because some swear by it.......