Elodea is also started to melt badly
Good fish choice and I like your wood as well.
What's the temperature in the tank. Elodea (Egeria densa) prefers cooler temperatures. I mean it's difficult to kill, but if it were to have a preference, cooler temps would be it. It did best for me in an unheated tank or outside in a tub when the overnight lows would go down to the mid 60s Farenheit. It gets a really deep, dark green then, with larger leaves, and delicate white flowers with yellow centers bloom above the surface. Very pretty.
llj