Neon Dwarf Rainbow ailment

[toffee67]

Here's a wierd one.

I havea a school of 8 neon dwarf rainbows along with other fish in a 37g tank. Recently I have noticed one of the rainbows has become very timid spending most of his time in the upper coner of the tank. He as also diminished to about half his original size. What's happening?

toffee67

 

[Lotus]

It sounds like he is sick. Are there any other symptoms? What are your readings for ammonia, nitrite, nitrate and pH?

 

[toffee67]

That's the only symptoms that are obvious. The pH is ~7.4 nitrite <0.05ppm, ammonia is 0ppm, any ideas?