In my limited experience, anarcharis requires a decent amount of light to do well. When I had very low light in my tank, it shed leaves, got very leggy and light green, and eventually the stems rotted out. Now, it is doing fine at @ 2wpg.
When establishing your tank, both hornwort and anarcharis function well as algae-busters, sucking up tons of nutrients that would otherwise contribute to algae groth.
Tho I will probably bid these 2 adieu due to overcrowding, I am reluctant to do so as they helped me out when I needed it. Pretty stupid to feel emotional ties to a 99-cent plant, huh?