Extremely low light and no fertilizers or CO2 sounds like great conditions for java moss to me. The most extreme of my own experiences was to use some in a tank that had no artificial light, no substrate and very few water changes. I set up an emergency tank early in summer for a few livebearers that I had not anticipated getting. I dropped in a handful of java moss just in case they dropped fry and to help with ammonia. The thing was set up on a card table in a room with a single northern exposure window. After 6 months, when I was finally ready to move the fish to a permanent home, I found that I had a nice large clump of java moss that was completely free of algae, not enough light for algae. In fact the clump of java moss was much larger than the original clump I had put into the tank. The stuff is absolutely indestructible, even by a non-plant person like me.