My perc never hosted at all until I introduced a yellow watchman to the tank. There wasn't a huge amount of agression, but definately some tension between the two. Since then, my perc started hosting in my frogspawn. My theory on that is the clowns use hosting as a defencive measure to keep safe from preditors. So if the clown is feeling non threatened and very safe in the tank, no need to host. Such as before the watchman/perc tiff. But let me repeat, that's my very unscientific and not well informed theory.
