Everything other than Elodea seem to wither out

I have a walstad tank (60x30x36cm*) with Vallisneria, Elodea, ludwigia, Amazon sword, Anubias. In that everything except Elodea isn't having any good time. All seems to be withering (leaves getting squishy and dissolves). Light 8 hrs a day, even without light it's closer to windows so gets some sunlight. . I also inserted couple of Sera fertilizer tablets.

I also see hair like stuff sticking to edge leaves which are hard to remove

Fishes: 6 serpae tetras and 2 small gold (less than 5 cm/2 in) fish (gifted by wife so can't give them away) few but perfectly fine.