N.Anomala swimming struggles.

[Dean Castle]

I need help please. My lovely male Nannacara is not swimming properly. He hides away most of the day except during feeding which he is doing ok. His pectoral fins seem to be ok but his tail fin is not moving much and he seems to move with his tail almost dragging on the floor. His female is looking after fry at the mo, and until a few days ago he was helping. Water parameters are fine and he looks healthy. Any ideas.
Thanks in advance.

Dean