Now that I have my new tank coming, I need to think about my quarantine tank. My book says, to make it 40g, do I really need one that big, if so I might as well just keep my empty 55g tank and use it. What do you think??
Hmm.... I'm not sure what kind of fish you plan on getting.... I've never used bigger than a 10gal. If you're gonna get gigantic fish, though, I guess you'd need a bigger one. A 20 would be nice IMHO.
I know some fish are better when added at the same time to avoid territory problems, so you would probably quarantine them at the same time too no? I know clowns are like this but im not sure about other salt water fish. Because of this you may need a tank like a 20.
If you've got the 55g laying around, you may as well use it. It would be preferable for the tang you intend to get. Most of the smaller fish will be fine with a 10 to 20g tank.
The only problem I can see is doing water changes on it, if that's needed with medications/treatments you're using. It's just a lot of saltwater to have ready/available. If you do have to use meds, you'll need to make sure you buy enough for that size tank. Sometimes that can get expensive.