Excellent. OK, first on the plants, those are the "Amazon" sword. Echinodorus grisebachii is the true species, though you will often find them listed as Echinodorus bleherae [sometimes they get the gender wrong as E. bleheri]. I will not go into the botanical explanation of the species unless asked.
These plants are the emersed form. Like all Echinodorus species, this one is strictly speaking a marsh or bog plant. In its habitat it spends approximately half the year growing emersed (roots in very wet boggy soil, leaves in the air) and this is when it flowers and produces seeds [it will not flower submersed, though this can sometimes occur]. The leaves are stronger and thicker, as aerial leaves of plants always are, to stand up without support and to resist loss of moisture. During the wet season when the forest is flooded up to 30 feet in depth for six months, the plant obviously becomes submersed, and the leaves die off and submersed growth emerges; these are the linear narrower leaves that you mentioned previously.
This species grows exceptionally well submersed permanently; not all marsh plants do, but this one is ideal. When this occurs, as in the aquarium, the emersed leaves will yellow and die as new submersed growth emerges from the centre of the crown. It taskes a couple months or so for this to occur. So don't worry when you see the outer leaves yellowing, provided new growth emerges from the centre of the crown. Leave the yellowing leaves a bit, as some of the nutrients are what we term mobile, meaning the plant can move them from old (dying) leaves into new growth. But eventually once the stem near the crown has turned brown so no nutrients can pass down, the leaf can be removed.
The size of the submersed leaves can vary a great deal. At this point in the story, I will get botannical but briefly. This species contains eight "variants" that until quite recently were considered distinct species:
Echinodorus amazonicus
Echinodorus amazonicus var. parviflorus
Echinodorus amphibius
Echinodorus bleherae
Echinodorus eglandulosus
Echinodorus gracilis
Echinodorus grisebachii var. minor
Echinodorus parviflorus
Haynes & Holm-Nielsen (1994) considered E. grisebachii to be the true botanical species, but many did not accept this due to the wide variety in leaf structure and size. But in 2006, the Finnish botanist Samuli Lehtonen carried out extensive phylogenetic analysis (using DNA, something rare previously) which basically supports the findings of Haynes & Holm-Nielsen, with a few changes, and this classification is now accepted. Dr. Lehtonen is probably the foremost authority on the Echinodorus genus, as this was the basis of his doctorate work and he has written several papers and articles. The synonyms listed above are the former “species” that are now deemed to be within the one polymorphic species E. grisebachii complex. Differences in appearance between these plants are apparent and seem dependant on the specific environment in the aquarium; this seems likely to also occur in nature, what can be termed transitional forms of the species. But the limited genetic variation within the complex is insufficient to establish reasonable groupings (Lehtonen & Falck, 2011). This species epithet grisebachii takes precedence over the others under the rules of the International Code of Botanical Nomenclature because it was the first name assigned to the true species, and this was by the American botanist J.K. Small in 1909; the name honours the German botanist H.R.A. Grisebach (1814-1879).
Hope that is of some interest. To your lighting, I would replace the Aqua-Glo with a Life-Glo (staying in the same series of Hagen "Glo" tubes) as it is much better light. And these plants will respond better under it.
Byron.
