hmmm i have not delt with Goldfish
laying eggs in a tank before,
only in the pond situation,so i don't know if i'm of any use to you.
in the pond,ususlly there is plenty of thrashing around in the pond plants,
usually in a shallow part,eggs are layed by the female and then a male will fertilize them,htey stick to the pond plants,
ususlly the other fish will come along and have a good feed,then
whatever is left will later hatch.i loved it.the babies were black in colour
and would later change to the gold colour we know,having said that
depending on the male who managed to fertilize to the colour the babies are.
not sure why yours were not fertile,unless you have no male.
really it could have been any of them,it will happen again,so it may be a case of watch this space lol.
i hope i have helped a bit. :)not really the answer i wanted to give you though.