It is somewhat of a hassle to deal with, but I've found duckweed to be a decent nutrient export in a low light tank, since it is still close to the lights. Other small floating plants as well have worked okay in low light and still grow kind of quickly.
Myself with a smaller tank I've found keeping a low bioload and keeping up on the water maintenance keeps the algae down. I have a 6g as well and we just change the water with RO water 25% per week and keep the water nutrient poor. There are only three small fish in the tank which keeps the bioload low.
Also I've found barley straw to work well as algae defense.
Any stem plant I've seen does poor in low light. But hygrophila is tenacious enough it may grow. You could try floating it in the tank if it won't grow from the substrate, it may if it's floating near the light.