Well if you only have a 20 gallon then i hope you know that you can not keep a tang or any type of surgeonfish in there. What would you like to know more about them? There is a ton of info on reefcentral or you can swing over to saltwaterfish.com and read more thread. Or you can try this site:
http://www.fishlore.com/profiles-tangsurgeons.htm
I just do not know how technical you can get with tangs, nothing like coral, but studying diseases is good. If you hydro everything before adding to DT you will not have to worry about disease, ich , and parasites....
Steffen Sparks