You don't have to place them in any particular place of your tank but they do need to be in an area of good water movement so sediment won't get lodged internally. You also should feed the tank with small particle food, the fans especially need to be fed often. If any of your sponges get sediment on them be sure to blow it off, i.e. your Yellow Ball Sponge looks to have sediment on it. Good Luck and it's great to see a young man interested in this great hobby! JMO