I got them past summer and left them grow further in same pot and substrate of the time before acquisition. They remain as much chlorotic as they were, when I obtained them. I will check with a soil tester pH and salt concentration in the substrate and I can not overstate the usability of such a tester. But before I proceed, I would like to read assumption by other members on the reasons of the chlorosis. Side notes: Substrate is peat based and I have already checked for sucking insects without any finding. 

45 minutes ago, Phoenikakias said:

I got them past summer and left them grow further in same pot and substrate of the time before acquisition. They remain as much chlorotic as they were, when I obtained them. I will check with a soil tester pH and salt concentration in the substrate and I can not overstate the usability of such a tester. But before I proceed, I would like to read assumption by other members on the reasons of the chlorosis. Side notes: Substrate is peat based and I have already checked for sucking insects without any finding. 

it looks like potassium or manganese deficiency.
i had once been shown this at a lecture, but unfortunately i would have paid more attention, then i would have known the exact differences and how to improve the condition of the plant. hope this is of some use to you 🤔

Potassium deficiency is manifested on older leaves and manganese one on the newest leaf.  Here seem all leaves uniformly chlorotic, which is intriguing, ruling out however not any kind of deficiency without further investigation. Entirely chlorotic can be a plant also because of too acidic soil or because of chronic iron deficiency, nobody can know for sure without soil analysis.

Iron perhaps

Looks like winter yellowing but that's not a diagnosis.  I would repot with fresh mix or, even better, plant out.  They will roar away over summer.

21 hours ago, richnorm said:

Looks like winter yellowing but that's not a diagnosis.  I would repot with fresh mix or, even better, plant out.  They will roar away over summer.

richnorm: that is very interesting and makes sense what you say. we used to have this more often even with most of the palm trees on the balcony, but since we have been fertilizing organically there again and again, just very very little in winter, this probably fell away. maybe i am wrong, but this could be accurate.