Nothing to do with Landscape Design.

wow, your plant is not dead, but it must be in shock from everything you're doing to it. :) It looks like it might be an Areca palm. I would cut away anything that looks black / rotten / mushy.

To be honest I’d bin that palm and start again.

Sorry, but it doesn't seem worth trying to save it at this point.

Wow this plant has been through a lot haha! It sounds like you’ve shocked and stressed it out leading to the yellowing leaves and leaf loss.

Does the black part of the root feel mushy or is it still firm?

After everything it’s been through, personally I would just leave it in the water and don’t mess with it anymore.

I wouldnt just throw it away as others have said, plants aren’t always about aesthetics but it is notably sad looking so give it a break and just accept it may not make it, but at least give it a chance :)

The bottom tip of the main root (as circled) still feel firm but it's all black. So you suggest not cutting it off?

Yes, the plant is still green, with yellowish leaves. More days have passed, it still looks more or less the same. The stems are still green. And the buds still do not unfold leaves.

So I wonder if plant dies with green roots as well?

Plants can adapt, since it’s gone from hydro to soil back to hydro it’s probably tried to change its roots to suit the environment but it’s a little worrying it’s black although rot would have softened it?

If you remove it, there’s a chance it may become infected or stress it out further since it’s the main root; but if you don’t there is also a chance it could start to rot and spread.

I think if it’s as firm as the upper root, personally I would leave it and check it every day making sure the black tip doesn’t soften or spread.

This might not be the best option if others want to weigh in but I think the last thing you need to do is make any more changes, just try to let the plant recover from transplant stress x 2.

Chloé

I’m definitely not ‘all about aesthetics’ and I seldom advocate chucking a plant out but this poor thing is in a terrible state. If you do want to try and keep it going I’d take the opposite route from Chloe and get it out of the water and into a fast draining mix ASAP. Remove any dead or rotten bits. Don’t overwater. Give it as much light as possible. Cross your fingers.

Hydroponics is a more complicated business than sticking something in water and pouring in a bit if fertiliser now and again.

Floral would transplanting again not cause further stress? (especially if it survived perfectly fine in hydro before and as OP states there is no mushy roots)

I didn’t suggest you did, at all, I just think if a plant stands a chance then it shouldn’t be thrown in the bin no matter how it looks.

I have several arecas but all in potting medium and none in water so best take the advice of floral (taking out of water, not previous advice of throwing in the bin) as clearly hydro is complicated, I was simply thinking of the amount of shock the plant is in and will potentially go through.

Chloé

I think it’s already under pretty much maximum stress and putting it into a suitable mix can only be a good thing.

Because it’s roots in a potting mix is its normal way to live.

What is "potting mix", I heard of it and I searched about it before, but I don't know how it is mixed.

So, Chloe doesn't suggest cutting the black tip, others suggest I should do so?

And, if I am to keep it in the hydro state for few more weeks, is my current water height suitable (as in the picture, with a red arrow indicating the level)

? And how long do you think I should wait before dumping it?