Hey Arapina and welcome to the forum! 
I know how easy it's very easy to become attached to fish, but the advice that you'll get on here from our members is second to none
Some members have been keeping fish for decades and are kind enough to share their experiences with us.
There are some smaller fish that are absolutely stunning that would be perfect for your size tank rather than the ones you have now. Or if you would like to keep your parrot then you could always get a bigger tank. I don't know much about some of the larger species of fish, but from what I can gather, once they start to mature then they can become very aggressive and will start to attack everything else in your tank, and this is why you could be loosing so many fish.
Also in regard to water changes, it's best to do one every week (it only has to be about 30%), and this will ensure that your fish will stay healthy and live longer
Your tank measurements show that your tank is about 54 ltrs which sadly is much too small for the fish that you're keeping at the moment. I have a tank the same size, and if you don't want to get a bigger tank, then I (and I'm sure several other members) would be more than happy to help you find some fish that are amazing to look at but would still fit comfortably in your tank.
I know how easy it's very easy to become attached to fish, but the advice that you'll get on here from our members is second to none
Some members have been keeping fish for decades and are kind enough to share their experiences with us. There are some smaller fish that are absolutely stunning that would be perfect for your size tank rather than the ones you have now. Or if you would like to keep your parrot then you could always get a bigger tank. I don't know much about some of the larger species of fish, but from what I can gather, once they start to mature then they can become very aggressive and will start to attack everything else in your tank, and this is why you could be loosing so many fish.
Also in regard to water changes, it's best to do one every week (it only has to be about 30%), and this will ensure that your fish will stay healthy and live longer
Your tank measurements show that your tank is about 54 ltrs which sadly is much too small for the fish that you're keeping at the moment. I have a tank the same size, and if you don't want to get a bigger tank, then I (and I'm sure several other members) would be more than happy to help you find some fish that are amazing to look at but would still fit comfortably in your tank.
