I realise this thread is kind of old ... but I anyway like to add a few comments:
Yes, they eat various algae, but as there are about 50 Goodeid species, their habits differ from species to species. Some are mainly carnivorous! Ameca
is a good algae-eater and Xenotoca
a fair one.
But, they can have a tendency to bite chunks out of the fins of other fish species, so I would not recommend them for a community aquarium. Maybe Ilyodon
would go well.
Also, besides algae they can also eat various plants, or at least they can damage growing tips of some plants. Again, this tendency differs between species. Ameca splendens
is critically endangered but not extinct in the wild. The same is for most species. A few only survive in aquaria.
In Europe, dedicated aquarists have established the Goodeid Working Group, in order to exchange information, experiences and (sometimes) fish. The main goal is to help these fish survive, both in aquaria and in the wild. I see no reason why people from other parts of the world wouldn't (or shouldn't) join, apart from the somewhat long travel distance to the annual meetings. In fact, there are members from other parts of the world already.
For more on these fish, see http://www.goodeidworkinggroup.com/