You cannot expect that plants that come from a normal aquarium water with pH around 7.0 will do at once fine in a blackwater aquarium with pH much lower. Lagarosiphon and Elodea and many (not to say: most) others normal aquarium pants are totally wrong in that kind of waters. Those named are dapted to hard waters and will soon die in waters wthout any measurable calcium and a pH of 6 or lower.
Ceratopteris is very good indeed and tolerates those waters if adapted over a certain period of time; then it is the best plant for small Paro-tanks. Limnobium is much less suitable.