Hi everyone! I really need your help please!

I've been growing a lucky bamboo that I moved from soil to water for over half a year and recently over a few weeks I'm noticing that it's roots are turning black.

It's not that they're rotting or anything, I've checked closely and there's no smell or mushiness and the leaves and stem seem healthy.

It's like some sort of black sludge covering the roots but it doesn't seem to come off if I wash it or try to rub it away. At first I didn't worry too much since it didn't come off and the plant seemed healthy otherwise, but I'm now seeing a hint of yellow on the tip of one of the lower leaves and I'm really worried if something's wrong.

I dunno how to explain it well with words so I've attached some pictures:

[

I didn't try to be too rough with the plant and occasionally just run my fingers through the roots to see if anything comes off and sometimes little bits and pieces come off if I scrub really hard. I've also been changing the water once every week since I first got it and only use boiled filtered water.

I'd really appreciate any advice! I really love this plant and don't want to have anything happen to it if I could prevent it.

A bit of backstory if it helps:

I got this plant around eight or nine months ago. Someone I knew gave it to me in a tiny plastic cup with rocks and water. I could easily tell that it was originally grown in soil and they had just picked it out and put it in the cup since the plant seemed way too big to fit in it and there was still soil left on its roots.

I was angry that they took it out of soil and was worried that it wouldn't survive the stress of being moved to water. But since I had no experience with replanting and water seemed to be the easiest method to maintain for a novice, I just hoped for the best and took it out of the cup, washed it and put it in a bigger water bottle cut in half filled
with filtered water.

I was really worried it wouldn't make it but after a few days I noticed it started to grow new "water roots". It was really cool to see them grow from tiny white threads to long beautiful orange roots.

Since then it's been doing well and has even grown a new leaf (though it's a little lighter in color). I've been changing the water routinely and occasionally change the container bottle.

But it's just recently that I've been noticing it's roots going black.
It started off with the main big root, which was the "soil root". Originally it was dark orange but soon it started getting darker and now it's pretty black as you can see.

One concern I have is if this "soil root" is somehow decomposing since it's not being used by the plant and is somehow affecting the other roots. But then again I'm guessing it would have happened a long time ago and I would have noticed some odor or some other sign. I've had this plant for months and it didn't seem to show any signs of distress or anything like that.

I really hope everything turns out ok and someone can help. This is the first plant I ever got and it really means a lot to me..

Sorry for the long post and thanks for any advice!