I think that is the correct ID as well. It is either a Strelitzia or Ravenala sp. (because of the leaf arrangement) and the actual leaf definitely looks like S. nicolai.This plant is Strelitzia Nicolai
I think they are submerged in the tank, take a look at 9:00 in this video. I assumed it doesnt rot since there are enough O2 in the tank?from what I can see, the roots are not submersed in the tank but rather behind it in soil.