Glowlight without a glow

[Blueaqua]

Hi,
I'm wondering if anyone can tell me why my glowlight might have lost its glow? Could it just be old age?
I have a large planted tank with an established biowheel and a range of community fish, tetras, plecos, catfish etc.
I have had three glowlights for over 18 months, they have been transferred between tanks, all three have allways glowed brightly. It has only been in the last few weeks that the colour of one has really faded. Is it just old age?
Ammonia, Nitrite, Nitrate and pH are all fine.
I have heard that you can get albino glowlights which don't glow as much, but mine has had a glow, but lost it!

 

[Harlock]

I have 5 head and tail light tetras and one is very obviously the alpha. He patrols the middle of the tank and if any of the other four get out of place (one hides behind a filter intake all day, one by my ozelot sword and two in the wisteria) he chases them back into their place. He is mean and nasty and likely killed the other one I had as I originally had 6. Anyway, the dominant one is the one that shows the most color. The others never look as good as he does. Maybe there is a hierarchy you've not noticed amongst your three tetras?

 

[Blueaqua]

I've been watching for dominance cause I thought the "glow-less" one might not be getting enough nutrition (he's I fair bit skinnier than the other two). But, there doesn't seem to be any.
The glow-less one is very shy and hides under the leaves of one of the low lying plants, or goes into the holes in one of the logs. The other two come and hang-out with him for a bit, but he doesn't play so they leave him alone. Certaintly no bullying.
When it comes to feeding time, he doesn't come to the top, he waits for the food to make its way down to him, but he is eating plenty.
Its got me puzzled!!

 

[blueturq]

He doesn't sound too good.

Also, with tetras or any other schooling type of fish, it's best to purchase AT THE VERY LEAST a school of 5, as it is less stressful on the fish, and it's also more natural.

 

[Blueaqua]

I started out with 6 glowlights in the original tank, but the other three died early on, and these three have lived, I haven't replaced the others cause I've been a bit concerned about my stocking rates in the new tank.
I used to have a separated tank with a decent bio-ball set up, now I've just got a normal tank with an external penguin 170. I've only had this new set up since the start of December.