Constant rot problems

[heavensent]

Hello,

I am having a very basic problem despite adjusting many aspects of its management. NO matter what I do every orchid I own starts rotting at some point... I have adjusted the watering heavily (going from 5 to 12-14 days). Every plastic pot has additional holes I made. I only use high quality bark substrate (from Substral). Humidity is always 40 - 55 %. Fertilizing happens frequently in very very diluted form... I make sure to let the water drip of so the plants are definitely not sitting in the water. They have huge SE window with plenty of light...

Where am I going wrong? I also remove the little sponges they have in their original substrat to avoid a wet crown... the last two I repotted at first seamed extra happy. All of a sudden, roots are starting to dry/rot?

There are no pests presents... my last thought is maybe hard water? Any ideas? I have a plant with four (4!) keikis with previous strong healthy roots that just started to rot in seemingly perfect set up...

Thank you!