This could be a little late in advise but I believe your plants are more of a bog plant than an aquarium plant. I had a simpler problem with what I thought was an aquarium plant. It did well for a while and then the old leaves died. The new ones came in but did not grow very large.
I have taken them out of the aquarium and have made a bog like aquarium. They are doing a lot better now.
I have taken them out of the aquarium and have made a bog like aquarium. They are doing a lot better now.