Normal Golden CAE gets 'blushing' gills after awhile?

[knifegill]

I have a golden CAE and after a few weeks in my tank, the metallic coloration in his gill plates broke down and I can see his pinkish, healthy-colored gills through them. Now and then some of the coloration returns but most of the time I can see his gills, just like in blushing angels and goldfish. My suspicion is that some kind of specialized opportunist that can digest those cells moved in and is making a living at the expense of my little guy. Has anyone else had their GCAE go blush on them?

Previous look:

See the redness around his eye? That is the color that now dominates his gills. And it's not symmetrical, either, since any given week there will be more missing on one side or the other.

 

[knifegill]

Bump? I know, you've probably never seen this condition before. Just hoping for anything about gills losing their metallic color cells and becoming see-through. Want a pic?

 

[knifegill]

See that creepy red line under his eye at the bottom of his gill plate? That comes and goes and is currently closing over. The other gill has returned to normal for now, too, but I expect the erosion to return, it always does.

 

[Bottomfeeder]

That's weird... have you done water tests?

 

[knifegill]

Yes, I test my water weekly. This is in my slightly overstocked ( ) 55g. The nitrates stay a little high, but I just added more plants. Besides adding an extra water change during the week and switching it out for my 75g, I am aware I need to do something. They're only at 40ppm, but I like it around 10ppm so it's a lot in my book. But aren't GCAE's relatively hardy fish? I wouldn't expect a little high nitrate to cause this, though I do admit the little bit of stress could open the door for whatever the organism is that's doing this. If it even is an organism.