In minuscule amounts---very---some corals will tolerate it. I had bubble, xenia, sponge and a wealth of inverts survive a shallow cycle and go on to grow in a working tank. I cycle simply with fishfood. Drop into saltwater/ro/di about 1 flake per 20 gallons, daily, until you see ammonia and keep at it for five days after you don't see it. It's a fairly gentle method and I was using rock from a broken-up tank, which had all sorts of life in it. No dieoff to speak of.