Supposedly floating plants are easy to take care of, but I can't seem to get any of the one's I've got to thrive. I have some red-root floaters and salvinia minima in my son's fish tank, and some salvinia auriculata in a quarantine tank, and in both cases the plants are slowly withering and dying. Both tanks are cycled. My son's tank has a betta, three bronze corydoras, and three Amano shrimp. The quarantine tank has four nerite snails, one large ramshorn snail and an unknown number of baby ramshorns. They both have HOB filters, but I made barriers out of plastic juice bottles to reduce the flow. Any ideas why these plants won't grow for me?

Son's tank water parameters:
Temp: 77
Nitrates: <20ppm
Nitrites: 0ppm
GH: 300+
KH: between 80 and 120
PH: 7.6-8
20210601_100223.jpg

Quarantine tank water parameters:
Temp: 71 (heater is currently off)
Nitrates: <20ppm
Nitrites: 0ppm
GH: 300+
KH: between 80 and 120
PH: 7.6-8
20210601_100115.jpg