They grow from propagule (seeds) about 6"-8" long.
You don't want to stunt their growth, you just cut back a little here and there.
I recommend cattails, water hyacinth and water lettuce. Plant the cattails in a pond or strawberry basket with pea gravel and make sure the water is flowing thru them. The other two are floaters with massive hair-like root systems. I have even used Anacharus in the middle.
Terrestrial plants were never all that great at filtering.
This is not a miracle cure but if you already have a sump it's a cost free addition.
My 60 g sump would have room for about 30g worth of plants, I might give this a try as well. My saltwater tank has a refugium with a lot of macroalgae and it seems to work quite well on my 120g reef (25g refugium). It seems that it is more difficult to setup in fw.
im sorry i should have expanded but i haveused this type of things on ponds and it has been used on ponds at these levels and worked. 10% was meant for a lower stocked tank but with very high light,fast growing plants and water changes i believe the lower end of what i said is possible.
but at the lower levels it can be used effectively as supplement to other filtration,just from the comment that the plant filter must be the same size or bigger than the tank.