I agree to your phosphorus def. the damage is done , and leaves will not recover. but we can stop it.You got to take care of the roots of the PLant. Think over your watering habits, 2 liters sounds like a very high number of water for one plant in 24 hours. Watch your PH. Phosphorus is absorbet around 6.2 PH. And as you already do give her some Phosphorus fertiliser. As i said the dmage wont heal but you an stop it. Happy growing