[ThRoewer]

I had the gas bubbles primarily with breeding male pipefish who had them in their belly fold. This was in rather dirty tanks, some with and some without skimmer.

To me opportunistic bacteria as the underlying case seem plausible. The primary location would fit some dirt getting trapped and starting an infection.
At least with my pipefish it was for sure not super saturation. If it was I would have expected to see males and females equally affected.

If it is caused by opportunistic bacteria, antibiotic treatment is unlikely to have a lasting effect.

Diamox treats the symptom, but not the cause.