Glass/Ghost/Phantom catfish issue

I have eight glass/ghost/invisible/phantom catfish. Poor things. They have no definitive name! There are two kinds of glass/ghost catfish, apparently. I noticed that one of them suddenly turned 'white'. Is there a ghost/glass/invisible/phantom catfish expert out there to advise whether there is something wrong with this fish? ((LOL!!!) It's a 75 g tank. I've had them for about four months. The parameters are perfect. Perhaps Casper has a disease peculiar to the breed. I noticed today, that another one is also turning 'white'. I'm certain that this is a 'Casper' issue. Photos were taken from my cell, three inches away from Casper. Apologies for quality.

 

I had these fish before. Turning White can be a sign of stress and illness. This one may pass away. Watch out.

 

I had these fish before. Turning White can be a sign of stress and illness. This one may pass away. Watch out.

I'm worried. Over the past few days, I see that same 'whiteness' on at least three other ghost/glass catfish, but to a lesser degree. I don't know what's going on. What is this?

 

I just spotted six of them and they all have 'whitebelly' to a degree. Is there any one out there that can give me info re this breed?

 

I had these fish before. Turning White can be a sign of stress and illness. This one may pass away. Watch out.

Nothing has changed in their physical environment. The only thing I know is that a particular species of mold (Cladosporium) grows in my water pipes.