In message , P Verstege
writes
Hello. I have a new 8' x 17' x 3' PVC-lined pond populated by 72
assorted goldfish/shubunkins and 3 koi. Around the outside of the pond
(on top of the overlapping liner) I have placed rocks. Some of these
are Cotswold sandstone type rocks I believe.

Genuine Cotswold stone is oolitic limestone found in the Midland region
of England.

I have some limestone, though not oolitic, in my pond without any
problems.

I must say though, you have an awful lot of fish in a pond of that size,
and they WILL breed too!

Steve Jackson