This was a response to a different post from Beth:
Formalin is formaldehyde. Very toxic treatment, particually to reef tanks. And, it is also ineffective for ich. You're wasting your time, and the health of your tank with this ineffective treatment.
The only effective treatment for ich is hyposalinity and cooper. These treatments need to be done in a QT. You can set up a great QT for $100. or less. So, why sacrifice the hundreds of dollars you have invested in your tank by using toxic substances in it? Do you know, that there are some states that won't even allow the sale of formalin because it is that toxic. Formalin should be used for short term bathes only and only for specific ailments, such as brooklynella and black ich.