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Where did you get these plants? The first pic is hard to identify, but if purchased from one of the major pet chains, it could possibly be mondo grass. A plant sold as aquatic, but will only live if allowed to grow above the water line. If it slowly wastes away to nothing, it could very well be mondo grass. The only thing keeping me from a positive ID is that the leaves don't look dark enough. If it is truly aquatic then I would say it is a type of Cyperus like the others have suggested.
The second plant is tricky for me because I don't know much about stem plants. I was thinking some kind of hornwort or milfoil but honestly it looks very similar to Pogostemon erectus.
Increasing your biodiversity increases your stability.
You know what this tank needs? ........................ Crypts.