I have one couple of apistos (triple red cockatoos) in a 20L which has driftwood, rocks, leaf litter and 3 caves. I have a couple of guppies as dither fish and to provide the occasional live food they like. The problem is, this female apisto who does not have eggs or fry to defend has claimed the whole tank as her territory and attacks the guppies relentlessly. She just bit a chunk out of his tail. I have 6 Otos coming and I sure hope she doesn't attack them. She never is aggressive towards the male. Any suggestions?