Root explosion with daily watering | root issues | Questions regarding fertilizing

[Cymbidium]

Hi,

for about 2 to 3 month now I've been watering one of my Vandas in a bucket of osmoses water over night for about 7-10 hours. Considering the weight in the morning it seems to suck in about 1 liter of water.
Additionally I've wrapped the roots in a few strands of Synthic to help keeping them moist during the day.

After just a few days of watering the Vanda as described I noticed new root growth all over the roots (see pictures). I've stopped counting by 50+. And I find new root tips every day. So they seem to like it.

Regarding the Synthic I just don't know. What I like is that they really seem to help a bit with keeping the roots moist. What I don't like is that they are not pulling water up the strand, so you need to soak them completely.
So I want to test some micro fibre as I've seen on YouTube.

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Unfortunately I've noticed a problem with two roots about 3 weeks ago. One root started to shrivel and got dry. But what kind of made me uncomfortable was that it had some black spots. So I decided to cut off the root. Of couse I desinfected the cutting tool and I also used peroxide on the root and let it dry for one day.
Then I started noticing that the root got a little darker when watering. And this darker part is starting to grow. Now I am worried that I might have a fungal infection or similar.
So, whatever is going on I guess I should have waited a few more days before watering it again.

What do you suggest? Should I use Physan 20? Cut it again and let it dry properly? or?

And then there's another root which also starts to blacken and shrivel. Is this just normal or something to worry about?

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And lastly: Fertilizer. I am really struggling to get a hang of fertilizing my orchids. I have quite a few different fertilizers (as far as they are available in Germany) and want to alternate them.
I've also bought a tool to measure the µSiemens.

A few questions which I couldn't answer myself so far.

How do I fertilize / what quantity of fertilizer does the orchid need?
a. Soaking the orchid pot for a few minutes in the fertilizer mix, similar as I water them.
b. Just using a watering can and adding "a bit" of fertilized water to the already watered orchid?
c. Just spraying the roots (vanda)
d. Spraying the leaves
e. ???

What strength /µSiemens should the water / fertilizer have?
I've heard so many different statements, like weakly weekly. But then also that this way the orchid might not get enough fertilizer. Then once a month in full strenght, but then also that this way the orchid won't have continious access to nutritions... What about the Vanda. So far I've only sprayed my Vandas with Orchid Myst every second or so day, without any negative or noticed positive effect. But as it is quite expensive I won't buy another bottle.
On the other side I've fertilized a cattleya with 250 µSiemens just by putting the pot for 2 seconds in the fertilizer mix and got a few burn marks on new roots after a few hours.

I've read so much and seen so many Youtube-Videos about fertilizing orchids, but still I don't really know how to do it properly.

Hope you have some advice for me.

Thanks!