Oh that's a good question.......
My mind was stuck on duckweed. But that might also be too much. Do you dose any ferts?
But if you got some shrimp in there, you never know... Its worth a shot adding some and seeing how your plants look.
No dosing yet, still looking to keep it growing mostly emersed.
We'll see how it goes! I had duckweed once in a bowl home to two African dwarf frogs that sat on my studio desk at college. The stuff seemed to double over night! Not a problem in the bowl though and the frogs did enjoy the cover.