I have dosed Exell (equal to Easy Carbo) with Vallisneria without problems - double dose, on the other hand, spell total melt.
As an oddity, I can reveal, that melted Vallis have re-grown on several ocations ( growing point had survived). Giant and Natans both did this.
- I would defenitely recommend the acclimatization, by slowly increasing dose, though !!
And it's worth remembering, that "Giant Vallis" cover quite a lot of varieties in trade - they might differ in toletance !!