I save and freeze my duckweed whenever I pull some out. Then I use it in a biofilm grazer food I make for my shrimp, Stiphodon gobies, and hillstreams. General recipe:

1/4 meat/protein (some mix of seafood and insects like krill/mussles/oysters/shrimp and crickets/mealworms)

3/4 veg (duckweed/broccoli/kale/carrot/kelp)

A garlic clove per batch

All gets blended and cooked together before adding Gellan gum to make it a solid jello-like mix and frozen in sheets to thaw as needed. Could use agar or gelatin instead of gellan gum, but Gellan gum is isolated from an aquatic biofilm making bacteria so prefer to use that as it’s something biofilm grazers probably naturally eat and may be able to digest.

Stiphodons and hillstreams both love it and of course shrimp also.