Just wanted to update on here as still concerned about my mirror carp. Even now the weather has cooled down significantly and obviously so has the pond temperature, the mirror carp is always still on the surface with her back out of the water. She seems very "buoyant". She can swim underwater, but when still, always seems to be at the top. She still eats really well and looks visibly healthy. Any ideas anyone?
I'm trying a couple of days without feeding the fish, apart from peas, to see if that makes any difference. In fact, I might pop in to my local fish centre at lunchtime to see if there might be a sinking food to use instead of floating sticks. I wondered if taking in a lot of air when feeding from the surface could be making the fish gassy?
She does get a little sun burnt and ends up with a whitening on her back and dorsal fin.
I will also get some salt to add to the water and do a water test.