Why not remove all of it? Years ago I had Duckweed
, it came in on some plants (often does). Looked fine for a time, then it also got out of control and kept jamming up my surface skimmers I then had on my filters. I just pulled it all out. Salvinia
is similar but it has larger leaves, doesn't reproduce quite so fast, and is more attractive. Or Ceratopteris is a good floating plant. Or Amazon Frogbit
. Or Pennywort allowed to float.
requires every single speck; if one tiny leaf is left, it will soon begin spreading.
Remember though that all floating plants are fast growers because they are close to the light source, can assimilate CO2 from the air which is 4 times faster than from the water, and are quick users of nutrients via the leaves more than the roots.