The tag multi-pet-families is currently applied to a broad set of questions, but I think some of them (especially different fish in aquariums) shouldn't be tagged with it.
Regards concerns about households containing multiple pets of the same or different species and their interactions.
While an aquarium technically is part of a household, I don't think this tag should be used when mixing different species in a constrained enclosure.
The tag itself carries a strong notion of pet-human interaction, due to the word families.
I still have a hard time describing why I think those aquarium question don't fit, but I
One idea would be to remove the "same species" aspect of the description, I think most of these questions should be tagged with the respective pets tag. Maybe the tag is not really useful at all, it doesn't add value to a lot of questions.
Tags are only useful if they describe something specific. Currently it is possible to tag every question that involves more than one pet with it. I doubt we want or need such a tag.