I have no magic answers.
I find Amazon Frogbit is really very Nitrate hungry, and partial to more Phosphate than is ideal, many floating plants are used in dealing with polluted water, in fact so polluted they can be harvested to improve water quality, fancy name, phytoremediation.
Light! If only we could agree here. I find rainbow lights a gimmick but others are convinced by them. Too much in duration is definitely not helpful, and most plants cope with short photoperiods (5-6 hours) of intense light if, if CO2 levels of around 10 ppm are maintained, water temperature isn't too high and the water is "clean" but not inadequate trace and macro elements are available.
Honestly, I find 10 ppm to 15 of CO2 maintained 24/7 works well for most plants. Levels of Nitrate that see Frogbit suffer are not detrimental to most stems. Even at less than 5 ppm of Nitrate in the water column most stems seem happy in bright light with CO2 around 10 ppm.
But our tanks vary, even mine vary. One is full of floating plants, one is full of stems recovering and looking great now I have removed floating plants. The former is medium light high nutrient, the latter, high light low water column nutrient.