Our older cat does not like this new cat (half grown). Right now, I have a separate, smaller litter box for the new one, but I'm wondering when I can go back to just one main litter box? I have had three cats sharing a litter box in the past, so I know it can be done with only two, but it's been so long, I just can't remember the "when." My older cat is hissing and growling at this younger one still (though not as bad as in the beginning), but has never attacked him (and I don't think that would ever happen). It has been a little over a week that we've had him.