Well a lot will say Anacharis/elodea. It will work but I don't like it. Just a personal preference, no real reason except it makes a tangled mess and really tries to stay at the top and not build a lot of bulk that would provide a lot of cover for fry, in my experience anyway.
I would say riccia is a good one because it grows really thick and can tolerate most light levels when floating. Some good choices would be frogbit, water lettuce and red rood floater. They will all put out a huge root mass that fry can hide in and they will suck up nutrients like NO3 and PO4 keeping your tank parameters a little better. They do require a little more light, well maybe a lot more but without a lid on the tank, they will soak up the light without obstruction.
If you have medium light or higher then I would really suggest wisteria for the fry. It will grow floating but if it is the only plant you will have a mass of plants that will hide any fry. Since I let mine grow again I have had 6 sword fry survive in the last month where I have not had a single one survive in the 6 months prior.
forum community dedicated to tropical fish owners and enthusiasts. Come join the discussion about species,breeding, health, behavior, aquariums, adopting, care, classifieds, and more! Open to fish, plants and reptiles living in freshwater or saltwater environments.