Hi,
Here is the info from Tunze.
""The 6201 will work on 220V 50Hz as is, he will only need a Euro plug or plug adapter""
So they should work. If you are in Europe, Asia or Australia then Tunze does have dealers in those areas, so you would need to go to them, otherwise could void your warranty.
If you are in another country, should be ok, but doing the plug conversion can cause some warranty issues.