if the water quality is healthy, all you need is fish poop. Poop equals fertilization. I never ever use any fertilizing chemicals in the tank. Let nature solve its own problems. If you give the plants 12 hours of sunlight and fish poop, you will be fine.
I have had natural sunlight coming in through the window for the last 6 months from the south window angle with mini blinds (regulate the rays), providing the plants plenty light, and with fish poop, the plants have flourished.
word of warning: unless you are absolutely sure of what you are doing, I would refrain from natural lighting from the sun; it can cause algae problems and/or overheat your tank - I have been able to prune the algae so the plants are competing on a natural level (I prune the algae every Sunday) and I do not have a heater in the tank during spring summer and fall seasons...it can be done, I've done it against all critics, even those who have been in this industry for decades...but again, unless you are absolutely sure or know what you are doing, I would just keep with fluorescent lighting and fish poop.
Also you may want to cut the dying back plant leaves, because the plant cell structure will struggle under the decay, that is, you do not want to lose the entire plant - just a few leaves or one leaf, understand?
So let the fish poop do its thing and get the right lighting, 12 hours on 12 hours off, and you'll be fine.
Let us know in a few weeks how it went, I look forward to your progress.