mathias,
Can you describe your watering practice in more detail? Also describe the soil. Is it dense and peaty or loose and gritty.
My initial reaction is that you are watering it improperly.
I have not tryed to over water it,but keep it moist so it doesnt dry-out.
At first blush this seems OK but I wonder if perhaps you have been watering it in small doses rather than really soaking the soil which is what you should be doing. It is possible that you are keeping the top of the medium damp but allowing the deeper material to remain dry for extended periods.
Water should not be rationed for fear of over-watering. Proper watering is more about frequency than quantity. Always water thoroughly until water flows from the drain holes. You could pour a gallon of water through your soil and this will not be over-watering. You get in trouble when you water too frequently.
I suggest you investigate deeper in the soil and try to determine if the core of the soil is dry. You may have to slip the tree from the pot to ascertain this. If you find that it is dry then you have been watering incorrectly and emergency measures are called for. Soak the tree in a basin of water nearly to the rim and allow it to stay there for 15-20 minutes or until the soil is thoroughly saturated.
Keep in mind that this is only one possible cause/solution. Get back to us and tell us what you find. Oh and pictures certainly would not hurt either.
https://www.helpfulgardener.com/forum/viewtopic.php?t=3724
Norm