root rot on vase culture vanda

[Oranagra]

Hi,
I have 3 young vandas in something like vase culture.
they are bare rooted and i soak them each night for some 8 hours in fertilized rain waster (~400ppm).
i used to soak them only for half an hour each day, but they don't have a lot of roots, and i was advised to soak over night.
they are all doing doing quite good, growing leaves and getting bigger, but the one with the longest roots (V. Pachara), had it's root touching the bottom of the vase (which stayed wet longer?), and it developed some rot on the end (and even middle) of some roots.
since then i've cut the affected portions, and moved him to a higher vase, but still some places on the roots are developing some type of rot.

when dry, it doesn't look that bad, but when it's wet it looks rotted, and it seems to spread.

please let tell me if i'm doing something wrong care wise, and what should i do with the rot? is that normal?

wet:


dry: