Sorry to say but your tank was a little young for nems, by doing 5% WC's you will only lower your trates 5% each time so you might want to try a couple 25-30% WC's to try to lower your trates. I wouldnt toss the rock unless it is contaminated, doing larger WC's will help to take care of the trates. It would help to know the actuall Ammonia, Trite and Trate readings and what lighting do you have and size of tank.