Film on liverock preventing corals to attach

So, I have had this hardly noticeable film on my liverockfor a few months now. You cant really see it unless you are looking for it. It makes me liverock feel slimey to the touch. I believe that thjs film could be preventing my leather corals and zoas from growing off their frags onto the rocks. I never really had this problem nor have I read about anyone having a similar problem. My nitrate and phosphate levels are undectBle on an API ( directions followed word for word). Anyone have any idea what may be going on? By the way, the liverock was actually previously dead liverock that I reseeded with some lfs biorubble. I didnt cook the rock before putting in my tank, i just rinsed it off in a bucket of RODI.