"Ms C. Peach" wrote in message
m...
Hi,

Two of my Koya (at least 8" long) have recently developed a grey mould
about 1" round on their backs.

Can anyone advise me on what to do? I have around 12 fish in total of
different ages and size. They have all been together for around two
years.

Chris.

You might ask at rec.ponds