@Amarnath: Fish tanks are really beneficial and they enhance prosperity provided they are kept at the right place. Living/Drawing room is an ideal place and preferably they should be kept adjacent to or next to the North Wall. Remember not to get it fitted within the wall itself else it will somehow limit the growth and one may also feel stressed and anxiety prone most of the time. You should keep it may be at a palm's distance away from the wall.
Yes Guppies are good. but like I said the total number of fishes in the tank should be even.