They, and water Hyacinths, also monocots, both compete for surface area with Aldrovanda, and prevent them from getting sunlight, also their roots don't always get directly under the Aldrovanda.
The best companion plants are those that are rooted in the shallow detritus layer, and have their roots spread out just a few inches under the Aldrovanda strands, or even better yet, commingled with them, and have long leaves and stems that rise well above the surface to allow full direct sunlight to get to the strands.
- Rich