I am going to jump in where angels fear to tread. I will preface this by saying I have never heard of Black Ich, but that is probably my fault. However, if it is a parasite, and if you have no invertebrates in the tank, I would suggest hyposalinity. I myself kept a FOWLR tank at 1.016 for about six months. I had no problems at all. The way I understand it that parasites are invertebrates, and they literally blow up under hyposalinity conditions. I am like Mikey, I tried it, and I liked it.
