@jredouard25
I'm afraid to say Byron is right, and you are wrong.
Fish have evolved to live in certain ways, in certain kinds of water, and to have certain patterns of behaviour. There is no way of changing this. It is
perfectly possible to know what kinds of problems are going to arise, if an experienced aquarist knows what fish species are present. Tiger barbs will always behave like tiger barbs, bettas will always behave like bettas, and African cichlids will always be very aggressive. That IS how it works.
The fish you have are not compatible, and they will never live happy or healthy lives together, even in a larger tank.
Just at the very basic level, you have fish that need soft, acidic water (the corydoras, betta and gourami), and fish that need it hard and alkaline (the African cichlids). Even completely leaving aside the behaviour issues, there is
no way you can keep those fish healthy in the same tank, it's just not possible.
Turning to the behavioural issues now, you do have multiple, serious problems, whatever you might think. Tiger barbs should never, ever, be kept with long finned fish like bettas. Bettas and gouramis should never be kept together, as they're very closely related and will compete for territory. African cichlids should, always and only, be in specialist Rift Valley set ups. They need such specific water conditions, and have such high aggression levels, that they
cannot be mixed with other fish.
You might also run into huge problems with your corydoras. As you cichlids get bigger, they're very likely to try and eat the cories. Unfortunately, corydoras have a spine on their gill covers that means they will get stuck in the cichlid's throat. You will lose both fish, if that happens, as there is no way of separating the two.
We're not saying these things because we're showing off, or we want to have a go at people. We say them because we care about the welfare of the fish, nothing else.
You are free to do exactly as you wish; they're your fish, your responsibility, and no-one is coming to come around to your house and force you to separate them.
But do, please, acknowledge that there are people who have more experience than you. Just as an example, I've been keeping fish for over 40 years, and have kept, and bred, every fish on your list, but I still listen to the experts, and know that I still have things to learn.
Dismissing someone's advice because you think they're taking things too seriously, or think you know best, is not the way to become a better fishkeeper, which is what we should all be aiming for.
