phalaenopsis roots are dying
 

Hi there guys. I am new to orchid keeping, so Im not really sure what is wrong with my orchids.. I am hoping you guys would be able to help :(
I did a fair bit of research before purchasing my orchids, so I water them once a week or less, only when the roots start going greyish green. I have re potted all my orchids after purchase as some of them came in bad medium. I use the orchid myst on the aerial roots once a week and everything seemed fine for the first few weeks after purchase.
But today after work I have noticed that one of the roots in the pot has gone greyish brown. Ive pushed my finger inside the pot and managed to get a hold of it and it was completely empty on the inside. I pulled it out and the top layer came right off, leaving behind only the stringy part. So I decided to examine the 4 orchids I currently have and I found, what seems to me like an early sign of some sort of fungi.
The purple orchid I have was in the worst shape when i bought it, the roots you see there were already like this, I assumed it was sunburned. That orchid is kept on the far right of the shelf and seems to have the most of that fungi looking web. The orchid next to it seems to have it also, but not as much. The other two seem to be fine, so my assumption is that it has spread from plant to plant?

In the other two healthy orchids I have found a few tiny white balls in the medium, could be something completely harmless but I thought I might as well ask.

So the first 4 pics are of the purple orchid, the fourth pic is showing that stringy fungi? 5+6 is showing the orchid next to the purple one and its dead roots. Its the same orchid which root i pulled out and it was a goner. The aerial roots seem really healthy though, thats in pic 7. Pic 8+9 are the weird white balls in the medium of two other orchids.
Oh I also live in Ireland, so the climate is pretty humid if thats of any help.
I am very confused by all this, it could be absolutely nothing, but I just wanted to make sure in case I will need to use a fungicide etc. Thank you very much guys for your time and help!

The white stringy stuff looks like mold of some sort. It does sound like you have some rotted roots (I'm sure they were that way before you got the plants) and the repotting was a very good idea. The leaf in photo 3 looks like it is on the way out, but that's ok, it's an older leaf and the new ones look fine. Force of nature. The dead roots aren't doing anything for the plant - the soggy stuff on the outside of the root should be cleaned off, you can leave a few of the stringy centers to hold the plant in the pot. But the new aerial roots are good and healthy, and once they are in good media new roots will gros... you do want to water them until they turn nice and green, then let things dry out for a few days - these orchids want a wet-dry cycle

Hi and thanks so much for your response. You see when I got the orchids I checked all the roots when I was reporting them and took off whatever I felt was not healthy. The orchid that is now getting rotten roots was very healthy when I got it and that was around Christmas time. I guess I still over watered them, but as long as its just root rot and no other disease then Im not as worried. As for the mold, would you mind suggesting any actions I should take to get rid of that?

I don't do much for mold except repot... You could drench the pot with a fungicide ( I don't know what you have available, I use Physan which is a quaternary ammonium compound of some sort. Others may have other suggestions. One thing about watering... rather than spraying, I would suggest watering very well (put plant under faucet, let water run through the pot), then let it dry out for however long it takes (my climate is dry and I would need to water perhaps twice a week, for you, you perhaps a week or 10 days). The running water serves several purposes - it washes salts and other undesirable stuff out, and also pulls air into the root zone. And since these are really "air plants" - in nature grow hanging from trees with their roots exposed to the breezes, that air is very important. Also, as they dry, air is also pulled into the pot as the water evaporates. Again, those roots are getting "humid air" more than "wet"