You need to treat the main tank as well as the fish if it is ich, and it sounds like it is.
Have a look at the ich photo and description on here:
Koko's Goldfish Diseases PageDoes this look like what your fish has?
There are 2 ways of treating ich:
1. Heat, salt and darkness. Heat the tank to 80F, salt it to a level of 3 tsps per gallon (adding 1 tsp per gallon every 12 hours, not all at once). Keep the hood light off and the tank covered with newspaper or a cloth. You should see an improvement within a few days but you should keep up the treatment for at least 7 days to ensure a complete cure.
2. Store-bought meds such as Rid-Ich or Quick-Cure. Regardless of what the label says, you'll probably need to repeat the treatment at least 2 or 3 times to ensure all the ich is gone.
NB: Melafix will not help; I would remove it.
Hope this helps.