Salvinia natans: fertiliser vampire?

[micmath]

I've noticed lately that the plants in my tank seem to be starving for nutrients, meanwhile I'm pulling handfuls of thriving Salvinia natans off the surface every week. Then it occurred to me that the Salvinia is on the surface so it has essentially unlimited light and CO2, and therefore can consume as much aquatic nutrients as ever becomes available. Is there no way the underwater plants can compete with the Salvinia no matter how much fertiliser I add?

 

[Nathaniel Whiteside]

I would have said it will be a problem with co2 if they're doing okay mate. Sounds that way to me.

 

[nayr88]

Would it be more likely that the floaters are blocking the light?