I had what they call a "Freshwater Snow-Flake" Moray Eel once. I can't remember the scientific name, but it was a beautiful animal - grey with small yellow dots, and a true moray species. At the time I bought it the LFS was hocking it as a true freshwater species. Although they can do fine in freshwater for a period of time, in the long run it is unsuitable for the animal.
So, I did what you are doing. I bought the animal and bought a cheap 10 gallon aquarium. Over the course of about two months (maybe longer) I increased the salenity gradually until it was the same as my saltwater tank. I have to say it was the best saltwater animal I've ever had. It was SO hardy. And not aggressive. It reached its full length of 3 feet and lived a decent life until a snow storm bested it.
Just increase the salenity slowly. You'll know if you are going too fast, because it will stress the fish out. If you take your time, the fish will never even notice.
I'm not familiar with a silver tipped cat, but make sure it can't fit into the mouth of an eel. The dorsal and pectoral barbs of a catfish can lock into place in an eel's mouth causing a disaster. (You're probably fine, though)
I would suggest finding a freshwater Moray Eel and just do it both at the same time. I think it is a much more attractive species than a SW SFE, IMO. Good luck!
