My fishes has been staying in this aquarium for several months. They're all alive and kicking. I can see their happiness in this small aquarium of mine. My friends whom I gifted such fish are sad because their fishes has died.
My brother who's selling these kinds of fishes told me that the aquarium shouldn't be cleaned very often. That might be the reason my friends' fishes died. That's why I don't clean the aquarium on a weekly basis. They're even multiplying.