Why do my plants seem to get destroyed?
I have around eleven to thirteen small fish, including Hypostomus plecostomus.
My usual temperature inside aquarium was around 26 - 27 °C at first but I quickly made a fan cooling system which took it down to 21 °C at night and 23 °C during daytime. I do not have any carbon dioxide system, but an ordinary air bubbler pump. I still haven't bought any fertilizer because I can't afford it till next week and I don't have any aquarium LED red/blue'ish light. The aquarium itself isn't in direct sunlight at any time of day, but is still near window.
My aquarium dimensions are 90 x 30 x 40 cm. The substrate is a mixture of coarse gravel and fine sand.
What should I do to revive my plants? What is the most urgent step I should take first?