I got a new hobby from end of last year, it is to maintain a small glass tank with grass and fish. before that, I alwasys called it as fish tank, but I see the senior people of this hobby are likely name it as Grass Tank, I agree because the grass, stone and small trees are more close to the nature enviroment and you will see the complete green scenery at first look, then you see the small fish swimming. there is another professional English word for this, it is aquarium (水族箱）. but Aquarium is normally larger than the one in a small living room, like the size of my apartment. 50x50CM is  big enough at the corner of my sofa.