I have four P. terribilis in an 80 gallon and they take up all the space they have, established separate territories for sleeping and resting, but share the center for feeding. While they are gentle frogs, do well in their own small group, I wouldn't chance mixing them with anything else. I just think it's best not to mix species, let alone different genera, at least until you have some personal experience with both in separate habitats. There may be problems with territory, intimidation, even if you don't see it happening, and stress, that you may not recognize until you have a dead frog and can't figure out why. My reasoning has always been that even if frogs come from the same area, they don't come from the same small area as a 75 gallon tank.
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Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
5 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
4 P. terribilis
4 D. reticulatus
4 D. castaneoticus