[NepNut]

Not recommended to use even if you rinsed throughly to get rid of any trace of sea salts and minerals. Corals are mainly calcium carbonate which will be eventually dissolved in acidic media that most nep prefer. When that happend, the pH of the media will actually become higher (ph >7 = basic) and that's is not what most nep prefer.

However, there's always exception to the rules, neps like N. northiana, N. campanulata and other lithophytic neps where it originally grew on limestone substrate, coral chips "might be" a suitable replacement for limestone.