OK my Girlfriends fish are Have a little bit of black on their fins, and im assuming its amonia burn... my suggestions are to do like a 50% water change and then get a new filter, or change the carbon? Would this be appropriate?... Currently i am having her salt her tank (help their slime coats)... any further suggestions?

Hope you all can help... Thanks

CHeers

If the black on the fins has just recently arrived, it's an indication that the
fish is recovering from ammonia burns. Water changes every couple days
will help even more. If the tank is established you really don't need
any charcoal/carbon in it. Other than that make sure to test the water.