Azolla works well for removing nutrients and you can always use a net to
remove surplus, COMPOST what you remove. I would NOT let it die off in
the pond in large quantities as the resulting decompostion may pollute
the water, it seems to go red before it dies off and at that point I'd
remove all that you can.
In my fish pond I use a the jet from a hosepipe to wash the azolla
toward my skimmer/outflowing stream.
In my heavily planted wildlife it doesnt prosper nor does duckweed. In
my plant and lily ponds it hasnt done well this year but duckweed is
doing ok.




--
sean mckinney