Sorry for being misleading. There are different types of plants, just like there are different types of animals, and just like animals, plants need appropriate care for te type of plant that they are. The plants I use are terrestrial plants that can handle having their roots constantly submerged. The plants in your lfs should be either aquatic, or semi-aquatic plants, that probably need to at least be partially submerged. The plants I am using do not add oxygen to the water, as their leaves are not in the water, however, for the same reason, they can get their co2 from the air and therefore grow much faster and use up much more nitrate than submerged plants would.