Vallisnaria may be off my list for high nutrient using plants. (though I'll keep the minis for looks) It seem that it may not compete with stem plants in nitrogen uptake from the water column (particularly nitrate). Being a rosette, it will rely less on the water column, more on the substrate. I'd like some Hydrilla, but don't know if it's available. It's very invasive in the US. Very competent stem plant. Often chokes out Vallisnaria in the wild!