I have got 3 goldfish that have been here about 6 weeks. One of them seems to be unwell but I don't know if this is normal behaviour or more serious.
I noticed about a week ago that it seems to sit on the bottom of the tank quite a lot, it will be very still for 5 - 10 minutes or so without moving before swimming off. It also seems tilt quite a lot onto it's right side. When it is swimming it is ok but as soon as it stops it starts to tilt.
The filter is quite strong and the tank isn't that big, When I put food in it swirls around quite quickly and if any of the fish get in the stream of water that is breaking the surface they get pushed around the tank.
My exMIL was over tonight and said she thinks it is fine but I am a bit worried about it.