Hi, and congrats on your new fish! Sorry to hear about the HITH, personally I wouldn't worry too much about replacing the biowheel, the jury's still out on how contagious...in fact I would try to treat the poor suckers if possible. (make sure to do lots of water changes and keep water quality crystal clear and perfect as possible, ie no toxins from waste or chlorineamine etc..., remove any activated carbon also..) Please see
http://www.cichlidfish.com/Adam/hith.htmljust to make sure they really do have HITH, you can also take a look at our ICH article at
http://www.cichlidfish.com/oscar2001/ich.htmlrelated post
http://www.cichlidfish.com/post17942.htmlgood luck and keep us posted.
Happy New Year!