I just bought an extra QT so I can dose copper in one and CP in the other (I'm crying internally). But I'm not going to risk CP with the wrasses, I already lost too many fish because of some ticking velvet bombs (Acanthurus tangs) that copper failed to treat.
However, just contact Seachem about MetroPlex today. This is what they had to say when I asked them how Metroplex works.
Thank you for your email. You are correct that Metronidazole is most widely known as a treatment for anaerobic bacterial infections. This is because anaerobic bacteria contain special biological processes that reduces Metronidazole, thereby "activating" it and making it toxic to those organisms.
In the case of Ich parasites, they have fermentation enzymes - one of which is a protein called POR. These enzymes are part of the parasites metabolism and POR conveniently activates metronidazole (POR is also present in most anaerobic bacteria). Most eukaryotes fail to activate metronidazole because POR is absent. Once it is activated it works very similar to how it works in bacteria, functionally disrupting the parasites DNA and ultimately killing them.
Sounds like a load of bs from seachem. Anything is possible and I'm sure there are a few strains of ich that could die from metro but it seems unlikely. I personally have never used copper. I work 10 to 12 hours a day so testing for copper is not easy and copper is very toxic to fish. It's a fine line to walk. This is why I treat prophilactically with every fish cp.
Sounds pretty promising, however 2 things. 1. I already bought an extra QT to dose CP and copper separately. 2. This was not tested on ich, but somewhat similar protozoa.