What's your tank like? Do you use ferts or root tabs? Do you have very soft water maybe?I hear this all the time. I can't get it to grow. Every emersed plant is doing great. My peppers are lush and have so many pods that the branches have to be supported. All my floating plants die. Slowly, but surely. I'll probably kill my hornwort as well.
I like gardening too, it's gotta feel rough when you're good at outdoor plants, then aquarium ones fall. Sorry mate, that's rough!