I was about to say that, The plants you bought are not true aquatic. They can live under water for a couple months but then will start rotting.
I had white ribbon that lived for 6 months then started rotting. I planted it outside, and it came right back. I cant believe the pet store sell's them when i went back to petsmart. i told him these are not true aquatic. And he say no there not. Im like what you no there not and are still letting people believe they are. And walk out the door with them. wow real nice