Maybe I will try Salvinia minima then...shame I really do love frogbit. One point their root were almost 2 inches...My guppies must be eating the plants. I'm definitely seeing less Frogbit now. :angryfireguppies just might be nipping the roots. I dont see any roots and thats odd because by now should have very long (10+inch) roots by that size
but as others said they do need alot of nutrients and light but they arent too picky, mine thrive with just nitrate and any flourescent light over the top of the tank if its at least 40watts of light. they could probably get away with even less light but I dont have any fixtures less than 40 so Idk
if you're having trouble with frogbi you might try to switch to water spangles
I use them in my unlit 0 fert 10 gallon and they love it
waterspangles and duckweed are the only floaters I can get away with giving minimal light and ferts
the rest will rot, and fast
I use a regular CFL light bulb...I keep it on every morning and sometimes at night until I sleep at midnight. No I don't keep Elasomas. I was one point going to keep evergladei species. :icon_winkAlmost definitely a lack of lighting. Look how the old and new growth is deteriorating in patches. It isn't a nutrient issue or you'd see either old or new growth symptoms not both. Dying roots are also a symptom of light deficiency.
Hard to make an exact comparison between your floating plant and a submersed grass plant, but have a look at this entry for light deficient Sagittaria, note the same sort of damage on your plants and on the Sag. http://deficiencyfinder.com/?page_id=720
What lighting do you have? How long is it on for?
Do you keep Elassomas? If so what species?