Well I keep my plant in a 1 gallon tank that I found and I have no light at all. Just ambient light from the window. And I keep snails in there which I never feed, and the water level is about half way because of lack of filling to the top. I sometimes put my water changing water in there as well.
Miraculousy the snails and plant live! I also stuck a cherry shrimp in there and its alive too... Strange creatures.
And yes I meant that the plant can help improve water quality. Of course all plants do that but this one does it better and faster.
And it seems you moved the plants more. And don't you think the photos look better without flash :-D.
And I can't answer your question for when to add fertilizer. I started dosing right from the start though. Someone more expert can answer it for you.