big octo in small tank
this is completely hypothetical, but this thread and others about large commercial aquariums that seem to keep GPOs and other large octos in small tanks got me thinking: one major difference between big aquariums and home tanks is that most aquaria have seawater piped in, and are constantly getting complete water changes. One reason TONMO recommends large tanks for cephs is the bioload, and it would seem like an open system that uses constantly renewed seawater would eliminate this issue entirely. Of course, perhaps the octos are feeling "cramped," but that's a harder call-- most octos seem to like small, enclosed spaces and little tidepools, although they also like being able to leave these hiding holes to explore... but perhaps they're not so unhappy in a small space if someone is bringing them food, and they always have fresh seawater?
Certainly, it is in the aquarium's interest to have a small enough tank that the octo is visible to the visitors, too, although it'd be a shame if they cause the octo to be cramped or otherwise unhappy just for this...