Dont manually remove it. That will do more harm than good. Those things spread like crazy. Any little bit left will grow into a new one.
If you have any kalkwasser, make a paste of that with some tank water. Then feed it a tiny blob of it with a small syringe or something. It will take it up as if its food, then melt away.
There are other methods of removal (ie: joes juice, epoxy, etc), do a search on the forum or google for more info.