I tried this with my own tank, and the result was not good. The chinese
algae eaters can and will take a shot at your goldfish. Don't know why they
do it . . . Don't know what other people have said about it (mostly not
good) . . . But I do know what I have witnessed first hand. These little
suckers are extremely fast when they attack, and a goldfish doesn't stand a
chance. My two GF have gained a lot of size since it happened, and both of
them still bear the marks from it.
I personally advise against it. They seemed friendly at first, but within a
few days, they started to attack the GF.

--
Kevin