Possible deficiency/humidity/pH problem

Sorry it was hard to cover the situation in a question - at the beginning I was using tap water with ~8 pH, which obviously caused these marks on the older leaves (they appeared much likely in a high RH environment) and I watered very slightly 2-3 times a day (I know I know, now I water every 2-3 days). I switched to rainwater which is usually around 6.0-6.6 pH. It made every new leaf look much better with some slight signs of older days, the plant had to adjust for a while. I kept the humidity at 55%-60%. When everything was ok, I started using some Bio-Grow fertilization, which brought back the problem. After noticing that, I stopped using it and went back to clean rainwater - everything was fine until this morning, when I saw the RH at 70% and these spots were visible on newer leaves once again... They re droopy because I shot the pictures just before/during nightime and I started some LST 2 days ago, so normally they don't lay on the ground ;)