[rsivertsen]

Hey Arvin, water lettuce (Pistia stratiotes) is actually in the fern allies group, along with Azola and Salvinea which reproduce so rapidly that they are illegal in several states here in the USA, considered as aggressive invasive exotics.

Some people use water hyacinth (Eichhornia), which are also illegal in some states for the same reason, are monocots, but their roots go directly downward, and don't get directly under the Aldrovanda strands where they can release the CO2 directly onto them.

Even decorative grasses can be used as companion plants for Aldrovanda and their roots will spread out from the bottom of their pots and get under the strands, and quickly absorb and assimilate the excess nitrogenous matter released by the captured prey. Leaf litter can also help control algae and is a food source for some zooplankton. - Rich