there's not just a chance of crossbreeding, there's also a far greater chance of interspecies agression with nasty results.
the males all need the same territory; the open water. they will fight each other, regardless of species and chase out the females too.
also: because of the 2 or more species, the groups per species are smaller. Cyps kept in a smaller group show significant more intraspecies agression than those kept in a large group
the best way to keep them in captivity is always to keep 1 species, 1 variety and as many as the tank can properly hold.
when you keep Cyps in groups well over 20 you'll see much better group harmonics. and hence healthy breeding females and undamaged males.
usually when I reply to this particular question I always get the answer "but they mix in the Lake!
yes they do. and to keep them succesfully in exactly the same manner, you'd need a lake sized tank too.
make it easy on yourself and on the fish: keep 1 species, 1 variety and buy yourself 30 or so. it'll be a really great set up and the fish will show their maximum coloration and do very well.
"And he piled upon the whale's white hump the sum of all the rage and hate felt by his whole race. If his chest had been a cannon, he would have shot his heart upon it"