I will second that harlock. Not sure what the metric demensions are, but in the states common depth "front to back" for a 20 gallon in 12". Stand against a wall and take one step forward. Now turn arround and take one step back. would you want to live your whole life with only that much room? I'm just trying to put it in perspective, not being rude or nuthin'.
generally folks who have a 20 gal will keep fish that stay small 1-2" adult size. HTH
generally folks who have a 20 gal will keep fish that stay small 1-2" adult size. HTH