How fresh are your seeds?
Nep seeds germination rate drops off very quickly as the seed gets old.
Are you saying you have the seeds on a rock based soil?
I have only germinated nep seeds a few times.
I used a plastic container with no drainage holes. Use long fiber Sphagnum as my soil.
I keep the soil extremely damp. I placed the container in my kitchen near a south facing window.
Had no issues germinating them.