Also, in your avatar, the spiky grass-like plant in the left corner? It looks like it could be mondo grass, which is not truly aquatic either. A lot of pet stores sell terrestrial plants as water plants. They'll last a while, but eventually, they'll deteriorate. If you gotten any, that could be why they are dying. That could also be part of the problem. Make sure to be careful when you by plants, especially from chain stores.
Some nonaquatic and semi-aquatic plants commonly sold as aquatic plants: