Help! Moping Glass Catfish. No Idea Why. What Can I Do?

[puppyduck]

Ok. So we have 3 glass catfish currently. We began with three, but after one passed away, the two left got along very very well, grew large and were healthy and happy. Until one of these remaining glassys got swimbladder problem. Sadly he died so we went and bought another one to keep Buster, the last remaining of the original three, company. This new glass catfish was a big boy, very outgoing, even ate from my hand on several occasions and the two seemed very chummy together. We then decided to go and get one more glass catfish to make another trio.

Everything seemed ok, but a few days after this new little fellow moved in, our outgoing catfish, Elmo, shyed away. We went away on holiday for a week an when we returned, we found him hiding away in the castle away from the others. He eats well as far as we've seen but he is no longer outgoing and cowers in the castle away from his friends.

I dont know what to do about him because he seems miserable. Would it be a good idea to get a final glass catfish to make two pairs (as they seem to be happier as a two) or is there anything else that could be causing him to be miserable?

Water stats are all 0, and good quality. All other fish are healthy. Tank stats in my sig.

Thanks for your help.

 

[Richie Hell]

Water stats are all 0, and good quality. All other fish are healthy. Tank stats in my sig.

By which we mean Amonnia and Nitrite. Nitrate is 10 ppm, pH is 7. Water is very hard.

 

[WILDER]

Your tanks slightly overstocked.
Any signs of flicking and rubbing, anything to go on, has he gone pale or darkened in colour.

 

[Richie Hell]

Nope. He's just started hiding away. He's completely changed since we came back from 5 days away.