Cardinal Tetra With Bulging Eyes!

[MissT]

I have 10, one of which has a something on the front of his face which is making it look like his eyes are bulging. One more than the other.
I watch them every day, up close, especially when I feed them and I haven't noticed anything prior to today. The other 9 are fine, as are the other fish in the tank and the one in question is still swimming and eating fine, schooling with the others and doing his usual things. There is nothing on any other part of the body.

Has anyone head of/seen anything like this before?

I can't take a picture as the buggers won't pose!

 

[N0body Of The Goat]

Popeye is one of the most common but tricky fish situations to deal with, as the symptom can be down to several causes.

Single eye "popeye" often suggests injury, which in most cases can be cured by using Epsom Salts (1 tablespoon per 5l) to draw out fluid and frequent water changes to keep the water in better condition.

Double eye "popeye" often suggests a bacterial infection, which can be cured using a broad spectrum medication like Myxazin.

 

[MissT]

We usually do a 30% water change every Sunday. However, we didn't do that this week, instead doing a 50% change Wednesday (15th) and a filter clean.

I have just tested the water again, and here is the outcome:

Nitrate - 40ppm (Same as the tap water)
Nitrite - 0ppm
Ammonia - 0.25ppm

It isn't the eye, it's above it, (the eyebrow area) but at different angles is looks like the eye itself and you can't see the blue of the eye when he swims toward you head on, and the other eye is getting a small bulge over it too.
The fact that it is 'spreading' to the other eye makes me think it isn't an injury.

 

[Prime Ordeal]

A photo would help but it definitely sounds like popeye. In fact it's the swelling of the head that pushes the eyes out. And your ammonia reading is no surprise as elevated levels are a certain cause of popeye. Treat with Myxazin as NOTG said or Interpet number 9.

You need to address the cause of the elevated ammonia though by giving the tank a good clean, reducing feeding, reducing stock or increasing filtration.