hey,
as suggested above, you should change your string to a heavier gauge strings (especially the bottom). Drop tuning that is as low as drop C will result in the the strings being slack. Adjusting the tremolo might help, but you might need to re-adjust a lot other things, like for example the action of the strings. Changing to a heavier gauge strings would be an easier and more practical ways, especially if you're not very familiar with guitar tweaking. Some people use lower strings as thick as 072! (Zakk Wylde, around there).
I hope it helps :]