I think you already know the answer to your question. If it says it is for terrarium use it isn't meant to be fully submerged in an aquarium. Some chain stores, such as Petsmart, sell a lot of plants that aren't suitable for the aquarium. If people don't read the fine print like you did they could end up with a plant that dies after a couple of weeks and get discouraged. See if you can take it back and get something else.