Yes, it's true that we are fully responsible for our pets and must learn well about what they need before making mistakes. But, I would not also say so absolutely that we cannot mix frogs. We just need to do that a clever way. Never mix animals of different sizes, from different habitat zones, species that can be poisonous....for example. There are also frogs, as Agalychnis Callidryas for example, that are very fragile and cannot stand any concurrency. But there are also species that are not difficult and easy to adapt. We also need to think about the fact that the space in our terrariums is much more little compared with the territory that frogs would have in nature and that some of the frogs are more territorial than the others. And, that sometimes we even cannot keep 2 males of the same species in one tank. But again, all this depend individually. Before mixing frogs, we need to study about all those and after - make a decision about possibility to keep them together. The best rule is - to keep together species that do not communicate a lot, for example - tree frogs and ground frogs….day frogs and night frogs….
Me, specially, I dream about mixing Bombina orientalis(I already have 4) with Hyla arborea(that I hope to find).
I will try to explain my choice and the way we must think

1-they require the same conditions of temperature and humidity;
2-they both are the same size (so they will not hunt each other and it will not be difficult to feed them – the size of food is the same);
3-they live on different floors, so they will communicate rarely (Bombinas spend all their time in water or near it, Hylas – are tree frogs;
4-Bombinas are active during the day, Hylas – during the night.
5-They do not look like each other so they will never try to breed together
One negative point – bombinas are poisonous if they are caught from nature, but they do not produce poison if they are bred in captivity and if they are not stressed. So, to avoid problems, we must change water more often and do not overpopulate the tank.
Another example: I try to keep together Litoria caerulea, Leptopelis flavomaculatus and Rhacophorus leucomystax. What I have seen. Adult Leptopelises are big enough; they have got a very big head and look like almost the same size than males of Litoria. But, I’m a little worried for the male of Racoforus because one of them stays little and I’m afraid that a female of a Litoria can eat him one day. For now they all live together since New Year. All of them support well. But, I would better keep Litoria caerulea with Polypedates dennysii that is bigger or with Litoria infrafrenata or with some of the toads the same size. I want very much to try to make a BIG terrarium with different species of Leptopelises(I adore these frogs) but need to see if they will not try to crossbreed. The same about different Litorias.
What I want to conclude, that we need to study, and then we need to try, and then we need to watch and react fast if something goes wrong

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PS: I’m happy to speak with people who share my passion!!!!Good that I have learnt English. Sorry for mistakes. I’m Ukrainian.
I put photoes of my terrarium and frogs. Want to say that it's better to have bigger terrarium for 6 frogs that I have:2litorias, 2racoforuses,2leptopelises