Goldfish seem to have an extra appealing slime coat. Anyway, I'm sure you'll try keeping them together. And it WILL work out for a while. There is no set time limit for something to happen. Some people have a pleco or sucker fish of sorts in with goldfish for over a year with no problem. Then one morning the wake up to a dead goldfish and the pleco or whatever feasting on it. And for as many of those instances, there are other people who have problems right away. The problem is that the ones who manage to keep them together for a year without problem, spend that entire year telling newbies that the two species can be kept together fine. Which to me is one of the most irresponsible thing, because as long as the fish are still together, there is still the potential for one to become a snack. I guess your stocking depends on how much you like your goldfish. Try it out if you want.