Hi,
yes, sodium is a problem.
Hardness itself is not a problem, but only if sodium is very low.
I do not have personal experiences with high sodium contents. There is a report on an Italian website (Acquariofilia Consapevole 3.0) with a list of plants that can thrive in high sodium levels (not a long list indeed), otherwise the only way is to reduce the amount of sodium using RO water.
The plants that are listed that can adapt to high levels of sodium are: Bacopa monnieri, Hygrophyla corymbosa, Hygrophyla difformis, Crinum calamistratum, Egeria densa, Elodea canadensis, Najas marina, Najas indica, Ceratophyllum demersum, Salvinia sp., Lilaeopsis carolinensis, Sagittaria subulata, Nymphoides aquatica, Cryptocoryne lingua, Cryptocoryne pontederiifolia, Cryptocoryne moehlmannii, Cryptocoryne ciliata, Microsorum pteropus, Samolus valerandi, Vesicularia dubyana, Taxiphyllum barbieri, smaller Anubias.
I did not tested these, but the font is a reputable one that is growing plants in brackish water tanks with very high levels of sodium.